[Development] redistributing QPA and platform style plugins

[René J.V. Bertin]

FWIW, I have bundled my modified Cocoa QPA and Macintosh style with the platform theme plugin I already had:

https://cgit.kde.org/scratch/rjvbb/osx-integration.git/

The nice thing with QPA and platform theme plugins is that 
- a platform theme plugin calling itself cocoa overrides the one provided by libqcocoa.dylib (but can still initialise an instance of the native theme or its modified version for proxying purposes)
- a 3rd party QPA plugin calling itself cocoa will override Qt's own version (or can, depending on its filename?).

R