Removed user data field from MyVertex, it's better to explicitly store and name all of the information previously held in this map
Added call to reset internal simulator data when Heal all is clicked. Closes #8.
Firther reduced occurences of user data stored in random string-object maps instead of in explicitly declared fields.
Closes #14.
Fixed bug where charts in toolbox on the right would change size on graph events. Closes #9. Closes #13.
Refactored Display so that when the graph is changed (e.g. load/generate) a repaint is forced on the VV instead of removing and re-adding all components. This means the panel on the right does not keep growing. Closes #9
Fixed problem with range of infected chart (max was 0 and it looked like the line was not there).
Merge pull request #17 from mbatchkarov/Plovdiv-9

Plovdiv 9
Changed keyboard shortcuts so that they work with Command key on the Mac and Control on Windows. Closes #10.
- Defined 5 vertex (node) types: Generic, User, Mobile, PC and AP.  Added custom icons for each type / state of the vertices.
The node type can be changed manually by clicking on the vertex label and selecting 'Change Type -> ...'
- (Experimental) The type of the vertex is initially determined based on the total number of connecting edges, after the graph has been generated.
- Added an option in the 'View' menu to change the zoom mode (direction) between  Mac OS / Windows scroll styles.