Fixes regression from 3a63bec39f (diff-31d7a50c99c265ca2793c20961b60979L4)
which meant listing templates doesn't work (rebar3 new help)

And more general namespace support

- Reworked the helpers for existing suites and expanded them
- Created a mock git resource module to test for its dependency fetching
- Added a test suite for dependency resolving with first checks for
  common cases (https://gist.github.com/ferd/197cc5c0b85aae370436)

Left to do would include:

- Verify warnings
- Verify failures
- Verify dependency updates resolving

code:lib_dir/1,2 can return archive directory for rebar escript archive
applications, rather than the application's directory in the project.

Add dependencies not listed in `applications` to `dialyzer_plt_apps`.

Removed separate compilers
Resolves apps to build
Finds avail deps before pulling/building
Includes relx
Simplifies build commands