Added a utility function (for tests) to drop collections in mongodb.
OPEN - task 26: MongoDB and keys as String 
http://github.com/markus1978/emf-fragments/issues/issue/26

Added a test-case for this issue, actually is not an issue.
OPEN - task 6: Model extensions 
http://github.com/markus1978/emf-fragments/issues/issue/6

Added the extension mechanism.
Added a first extension for statistics. 
If statistics are recorded or not is configuratbale through the
`EmfFragActivator`.
OPEN - task 27: Exceptions in EMF-Frag editor when selecting objects 
http://github.com/markus1978/emf-fragments/issues/issue/27

Fixed the clicking on statistics exceptions.