ExtModule's lacked support built in support for providing (#1154)

* ExtModule's lacked support built in support for providing
the verilog source. This changes creates traits that
can be used with ExtModule to provide the support currently found in
BlackBox

- Add support for ExtModule helpers
  - HasExtModuleResource to use addResource
  - HasExtModuleInline to use setInline
  - HasExtModulePath to use addPath
- Add tests of the above support.
  - Note: These tests use Stage instead of Driver
- Added ScalaDoc for HasBlackBoxInline#setInline

* Fix the danged trailing commas.

* Change to use `.transform` as the correct API for `ChiselStage`