[libmlocale] Deduplicate mlocale_defines.prf.in.

There's a lot of repetition here that makes it hard to see what's going on.
[libmlocale] Fix wrong path in .pc file for includedir
[libmlocale] Change install targets for Qt 5 and add packaging for Qt 5.
Merge pull request #1 from rburchell/master

Qt 5 support