Fixed issues #129, #135
Small refactorings.
Intermediate results: Revised feature model editor, to be consistent
when switching tabs.
Revised feature model editor.
Now, pages should be consistent at any time. 
When leaving the source-code page all edits are now bundled to a single
operation that changes the internal feature model.
This operation also works with undo() and redo().
Small bugfix for dirty state in feature model text editor.
Merge remote-tracking branch 'trunk/issue_129'

Conflicts:
	plugins/de.ovgu.featureide.fm.ui/src/de/ovgu/featureide/fm/ui/editors/FeatureDiagramEditor.java