Coverity fix: Fix possible illegal memory access

Details:
uninit_use_in_call: Using uninitialized value p.code when calling
VisitorState.
uninit_use_in_call: Using uninitialized value p.line when calling
VisitorState.
SVN_SILENT made messages (.desktop file)
SVN_SILENT made messages (.desktop file)
Hide custom buildsystem KCM from generic manager.

The custom buildsystem configuration is not used by the generic
manager, and thus just confusing our users. See discussion on our
ML whether we should get rid of the generic manager and just merge
it with the custom buildsystem.
Merge remote-tracking branch 'origin/4.6'
Port compilers to factories. Try to make it possible to add new
compilers manually.
Make it possible to add new compilers for the project parser.

Now we can globally add compilers and choose needed for the selected
project afterwards.

REVIEW: 118718
Add tests for CompilerProvider.