Get multiple selection working and highlight selected.
Add selection box and fix a bug when changing the state from multiselection to a create class/relationship
Merge pull request #22 from Zedzap/Selection

Get multiple selection working and highlight selected.
Merge pull request #23 from Zedzap/SelectionBox

Selection box
Merge branch 'master' into undo_redo_memento

Conflicts:
	src/WackaUML/WState.java
Merge of undo_redo_memento into master