- Rewrote diagram editor input handling in ActivitiDiagramEditor by
removing coupling to data- and diagram file.

- Introduced subclassed editor input ActivitiDiagramEditorInput that
references both data- and diagram file

- Made sure the newly subclassed version of the diagram editor input is
used when generating diagrams (either automatically via Eclipse IDE or
by wizard).

- Rewrote Matching Strategy so it correctly matches open editors, e.g.
by clicking the appropriate arrow in the preferences of a call activity. 

- Reactivated arrow in PropertyCallActivitiSection as a basic start.
* Modified correction to remove internal Graphiti API reference when
  creating a transactional domain.
  
* Consolidated constants into a class ActivitiConstants.java in the 
  utils project and let various other files now point to it rather than
  directly specifying things like extensions or texts.
  
* Modified Properties for asynchronous support. They used the wrong 
  event type FocusEvent of input fields. Rewrote them to use check 
  boxes for their boolean representation and used a SelectionListener
  instead so modifications only occur, when a selection/deselection
  occurrs.
  
* Implemented Call Activity Property selection. This will allow to open
  the appropriate process model when it's ID is found in one of the open
  projects in the Eclipse project explorer. In case multiple processes
  are found, the user is asked to select the one to open. 
  
* Created new package dialog in the utils package to host a modified
  version of the ResourceSelectionDialog, cause this one does not 
  support setting an initial pattern. This refers to bug 36029 in 
  Eclipse, where the appropriate method was available in Eclipse 3.3
  but is no longer existing in Eclipse 4.2.
* Added NATURE_ID to ActivitiConstants.java in utility project and
corrected various references to use it.

* Finished implementation of PropertyCallActivitySection.java:
** Automatically checks the process ID and if found in any open diagram
in any open project enables the appropriate button to open the diagram
** In case the user selects the button to open the diagram but the ID is
ambiguous, a dialog opens to select the diagram to open
** Added another button to select a process by process ID from any
available open project

* Added context menu feature OpenCalledElementForCallActivity.java and
introduced it in the ActivitiToolBehaviourProvider.java. It allows to
open the diagram referenced by the process ID given in the Call
Activities 'Called Element' property in case it is unique (the
non-unique dialog is currently only available via property sheet).
Moved from FocusListener to ModifyListener