add definition of 'COMMON_TEST' macro to eunit provider

The idea is that given we accept arbitrary config items for CT, we
should similarly be able to pass unsupported options and keep things
running.

However for unsupported options, a warning is very useful to have.

this ensures the project apps are compiled to `lib/` instead of `extras/`

this allows repeated test suite names across apps without conflicts

previously rebar3 dropped suites declared at the root of the project (via
`--suite=whatever_SUITE' probably) and warned. this was because the compiler
would recursively copy and compile everything in the directory indicated by
the test suite. this changes the copy mechanism to only copy erl source files
and directories that end with `_SUITE_data' into the `extras' dir in `_build'

when `ct_opts`, `eunit_tests`, `eunit_first_files`, `ct_first_files`, `erl_first_files`,
`eunit_compile_opts`, `ct_compile_opts` and `erl_opts` have values that are single non-list
terms warn and try wrapping them in a list when processing them in the `eunit` and `ct`
providers

This uses cth_readable to:
- silence error_logger output to the shell unless a test fails
- silence ct:pal output to the shell unless a test fails

I have currently not baked in any way to disable this behaviour, but I
figured if it is required, there is time to do it before the final
3.0.0 release.

* remove partial support for ct `test_spec` until it can be done properly
  and warn if `test_spec` is present in test opts
* use new compiler functionality to reduce complexity of provider
* reduce command line options available to those that can be
  supported properly

at the cost of some SASL warnings this prevents rebar3 from terminating
processes when reloading their code before running tests

* modify compiler interface to work on either application objects or
  directories containing source files
* compile all sources in `src_dirs` to the application `ebin` dir and
  all sources in `extra_src_dirs` to a directory mirroring it's
  position in the app's `_build` directory. for example, `apps/foo/more`
  would compile to `_build/default/lib/foo/more`
  for `extra_src_dirs` in the root of a project with multiple
  applications (so orphan directories that don't "belong" to an
  application) compile to `_build/default/extras/more`
* copy directories specified in `extra_src_dirs` into the `_build`
  directory so tools like `ct` and `xref` that expect source to be
  in a particular location still work
* clean compiled artifacts from all `extra_src_dirs`
* alter `eunit`, `ct` and `cover` to work with the new directory
  structure
* billions of new tests

fixes #788

to itself so a selective receive can be used to retrieve it

fixes #547

when running `ct` tests

fixes #513

- Crashes in providers lib when no providers in a namespace are bare
- Making sure bareness matches semantics; i.e. a bare provider is
  visible, a non-bare provider is hidden.

adding it results in ct test suites being compiled before they're
properly copied so changes made to suites between runs are not
reflected if a run fails before test dirs are copied

rather than profile root

fixes #415

to prevent any data from being overwritten

fixes #395

fixes #331