Trying to add a context menu ...
Fixed the context menu.
Added basic code for the handling of the last selected positionable tag.
Fixed the newly added private variables in (hopefully) all changed files; Made moveAction local to AnnotationDialog::ResizableFrame::mouseMoveEvent; Removed the unnecessary emptyTag from Dialog
Reverted the private function names back to the no-underscore version.
Changed lastSelectedPositionableTag from an item pointer to a QPair, so we can work on sanitizing the positionable tag candidate management.
Recovered the original functionality, simplified tag handling and removed the now unneeded deleteLastPositionableTag() function from Dialog.
Changed the handling of (de)selection of positionable tags to a more general way. Also did some code cleanup.

Conflicts:
	AnnotationDialog/ImagePreview.cpp (whitespace-only)
(Hopefully) changed the added code according to the kdelibs coding style.
Some further coding style cleanup