This change makes it so umbrella projects get ordered in a way more
in-line with what we do with non-umbrellas.

For example, a non-umbrella app (rebar3 itself) gives output like:

    └─ rebar─3.8.0+build.4270.refaece1d7 (project app)
       ├─ bbmustache─1.6.0 (hex package)
       ├─ certifi─2.3.1 (hex package)
       ├─ cf─0.2.2 (hex package)
       ├─ cth_readable─1.4.2 (hex package)
       ├─ erlware_commons─1.3.1 (hex package)
       ├─ eunit_formatters─0.5.0 (hex package)
       ├─ getopt─1.0.1 (hex package)
       ├─ hex_core─0.4.0 (hex package)
       ├─ parse_trans─3.3.0 (hex package)
       ├─ providers─1.7.0 (hex package)
       ├─ relx─3.28.0 (hex package)
       └─ ssl_verify_fun─1.1.3 (hex package)

The current (prior to this patch) output for an umbrella project looks
like this:

    ├─ bootstrap─0.0.2 (git repo)
    ├─ dirmon─0.1.0 (project app)
    ├─ fake─0.1.0 (project app)
    ├─ file_monitor─0.1 (git repo)
    ├─ peeranha─0.1.0 (git repo)
    │  ├─ gproc─0.5 (git repo)
    │  ├─ interclock─0.1.2 (git repo)
    │  │  ├─ bitcask─1.7.0 (git repo)
    │  │  │  └─ lager─2.1.1 (hex package)
    │  │  │     └─ goldrush─0.1.6 (hex package)
    │  │  └─ itc─1.0.0 (git repo)
    │  └─ merklet─1.0.0 (git repo)
    ├─ recon─2.2.2 (git repo)
    └─ uuid─1.5.0 (git repo)
       └─ quickrand─1.5.0 (git repo)

Which kind of looks odd because the layout represents the dependencies
of deps as declared by the rebar3 config files, but mix up the project
apps as dependencies. This turns out to break expectations, and some
external tools (such as Blackduck's dep detection -- see
d8a0f2281a/hub-detect/src/main/groovy/com/blackducksoftware/integration/hub/detect/detector/hex/Rebar3TreeParser.java)
which were developed with regular apps in mind, but not umbrellas.

This PR changes things by reordering all project apps at the root level
and putting them first, and then indenting all deps below them. The same
app now looks like:

    ├─ dirmon─0.1.0 (project app)
    └─ fake─0.1.0 (project app)
       ├─ bootstrap─0.0.2 (git repo)
       ├─ file_monitor─0.1 (git repo)
       ├─ peeranha─0.1.0 (git repo)
       │  ├─ gproc─0.5 (git repo)
       │  ├─ interclock─0.1.2 (git repo)
       │  │  ├─ bitcask─1.7.0 (git repo)
       │  │  │  └─ lager─2.1.1 (hex package)
       │  │  │     └─ goldrush─0.1.6 (hex package)
       │  │  └─ itc─1.0.0 (git repo)
       │  └─ merklet─1.0.0 (git repo)
       ├─ recon─2.2.2 (git repo)
       └─ uuid─1.5.0 (git repo)
          └─ quickrand─1.5.0 (git repo)

Now the project apps are back at the top, and all the dependencies
follow at one level of indentation below.

There is no recorded change for single-app projects.

- removed deprecated maintainers field from config template in
  rebar_prv_packages

This switch aborts the rebar3 run after the first test failure is
reported.

Since Common Test does not support this feature and it can be useful for
interactive development (a demand from one of the teams I work with), I
decided to add the feature as an experimental CT hook.

The hook notices any test failure, and forcefully aborts the current
script execution, but only during the initialization phase of the next
test; this ensure that all other hooks for a post-test failure have the
time to do things right.

The CT logs _will_ be interupted, and hooks of all kinds may also
suffer.

Since this might be a bit tricky to support internally, I will be fine
with a review that results in "no, Fred. Please test this in a project
plugin first" or if I get told to use profiles to mature the feature
(i.e. `rebar3 as failfast ct ...`) with a custom hook declaration.

For issue https://github.com/erlang/rebar3/issues/1974
Revert "add rebar.lock to template gitignore"

This reverts commit 8fb8a91130.

For issue https://github.com/erlang/rebar3/issues/1974

- fixes systests on darwin where previously the recursive cp would fail
   due to everything being copied after the last forward slash.
   Specifically, everything in  `systest/all_SUITE_data/` would be
   copied but not `all_suite_data` dir itself which the tests expected.

mostly copy/paste from rebar_compiler_erl

- Added support to rebar_prv_xref for filtering out whole module. A
  module may now be added to the list of xref_ignores in rebar.config or
  via -ignore_xref() module attribute
  - Added unit test for whole module filtering support to xref CT suite

The app data, when set by `rebar3_app_discover` basically does not
include the modules if it was derived from the .app.src file, even if at
a later point the modules were compiled.

Since there is currently no clear way to add that information reliably
across all compiler versions in all types of compilers, we simply clear
the cache and re-derive the information when required.

This might have a small performance cost, but is required for
correctness whenever an application's first build is run. Specifically,
this bug was detected when a plugin included lager's parse transform,
and the application itself also required it, but two distinct versions
were needed.

This patch finalizes fixing this issue.

Compile time with parse transforms needs to have the deps first in scope
before the plugins

Due to building dependencies with potential artifacts such as parse
transforms or macros, project builder plugins should be included in the
path, but _after_ deps are loaded.

Doing otherwise means that if any of the dependencies is required at
compile time, those of a plugin might get used first.

The old path handling routine would force loading a bunch of
applications, but it did not necessarily unload them aside from specific
calls that the other test handlers used to need to do, but no longer
needed under the updated path management of 3.7.0.

The leftover calls in the cover compilation bits caused some apps to be
loaded and to remain loaded before tests started.

Signed-off-by: Fred Hebert <mononcqc@ferd.ca>