Show Qt5 compability

[xhochy]

As Qt5 gets more mature and a lot libriaries are/will be currently ported, it would be nice to show if a library supports building and running with Qt5.

[cornelius]

As a generalisation it might be helpful to state something like a minimum Qt version for cases where libraries make use of features which are not available in all Qt versions. Maybe something like an array of minimum Qt versions or splitting manifests between Qt 4 and Qt 5. Given that Qt 4 is not really supported anymore this might more be a question for a future Qt 6. Needs a bit more thought.