* Refactored FileService.java from eclipse project to DiagramUtils.java
in utility project so it can be used in the gui project too (e.g. for
the collapsable sub-process). Applied the change to all necessary files.
 
* The FileService.java refactoring made it necessary to move the diagram
editor input to the utility project too.

* The previously introduced ActivitiResourceSelectionDialog in the util
package was based on the deprecated ResourceSelectionDialog. Removed
this depreation by using the FilteredResourceSelectionDialog in
PropertyCallActivitiSection.java in the gui project.