Add cut/copy/paste functionality.
I created a new Edit menu in the GUI. There are new buttons in the edit menu for each operation.
Each operation calls the same ID in the Diagram controller.
The diagram controller gets the currently selected items from the WContext.state.getChildren function which is based on selected elements.

I changed WState from an interface to an abstract class so I could have a default getChildren that returned an empty set.
Added delete option to edit menu.
Corrected issue where the movingAdapter for classes and relationships was still pointing to the copied element when pasting.
Properly clone elements on paste.
Merge pull request #26 from Zedzap/copy_paste

Copy paste