[LMP] Removed TransitionTime option stub.

No easy way to support this with gstreamer and playbins. Probably joining
two playbins with a padder will do, but that's too much work for such a
little feature I'm afraid.

And phonon-gstreamer seemingly doesn't do it too, neither does anything
playbin-using.
[Core] Use QToolButton instead of QAction kludge for main menu.
[Azoth] Avoid non-needed call.