[mlite] Enable building of a Qt 5 package.
[mlite] Compatibility fixes for Qt 5.
[mlite] Automatically generate .pc versions, add a Qt 5 .pc
[mlite] Gather version information from rpmbuild, or from git.

This avoids the requirement to make version bump commits, and is generally less
error prone.

Thanks to Bernd Wachter for the idea.