Bugfix: Properly check for language in RC files

Update the check for language in RC files to be ok if is globally set and
the actual block doesn't have one or is set locally with the correct one.
Bugfix: Properly append comments

Comments were not appended because of wrong variable name.
Cleanup: Use pass instead of continue

If we get here we already know that is a block that must be ignored,
so there is no need to check for other types.
Ignore one line comments ("//")
Ignore TEXTINCLUDE sections of Visual Studio Editor
Cleanup: Remove unnecessary commented code
Tests: Added several tests for RC format
Added a test for rc2po converter.
Tests: Several cleanups in RC tests

* Move tests to a class,
* Use helper method to avoid rewriting the code to write and parse a
  dummy file,
* Rewrote code to use explicit assertions instead of iterating in a loop.
Tests: Add method to check RC roundtrip conversion

Still not used, but already available for future use. This method is
now format agnostic, so moving it to a superclass in order to reuse
it in other test classes is advisable.