• Split MLT Qt plugins into their own ports [1]
• Cleanup the Python slave port [2]
• Bump PORTREVISION.

[1] Ports can now force the dependency on Qt plugin, which is needed

by Kdenlive. Having two different (conflicting) versions will help
with the transition to the KF5-dependent Kdenlive.

[2] Creating slave ports for other SWIG bindings should now be easy.