Several minor Palette Drag&Drop issues

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Source: Issue 2 (Pre-Google Code todo List)

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Problem A:
1.) drag&drop an entity from palette to diagram
2.) click in palette
3.) UNDO last action
Expected: insert into diagram should be undone
Instead: Element in palette moves around, inserted element stays on diagram

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Problem B:
1.) drag&drop an entity from palette to diagram
2.) UNDO last action
3.) REDO last action
Expected: element is inserted as expected (because undo has been redone)
Instead: element is inserted, but at the upper left corner of the diagram

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Problem C:
1.) drag&drop multiple entities from palette to diagram
Expected: both elements are still selected on the diagram
Instead: only one of the elements is selected (although all elements are 
correctly added to the diagram)
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Problem D:
1.) drag&drop multiple entities from palette to diagram
2.) UNDO last action
Expected: the whole drag&drop insert command is undone
Instead: only the selected element is removed, but the other elements stay on 
the diagram

Original issue reported on code.google.com by AFDiaX on 3 Oct 2014 at 4:02