OPEN - task 24: Default extrinsic ID for objects with indexed features
or indexed classes 
http://github.com/markus1978/emf-fragments/issues/issue/24

OPEN - task 6: Model extensions 
http://github.com/markus1978/emf-fragments/issues/issue/6

Added internal emf based base class `FInternalObjectImpl` that can store
ids. Thus we are using intrinsic ids and no extrinsic ids anymore. Most
test already run. Configuration for priliminary and defaultmodel ids are
not necessary anymore, since `newUserObjectsCache` objects can also
manage ids.
OPEN - task 24: Default extrinsic ID for objects with indexed features
or indexed classes 
http://github.com/markus1978/emf-fragments/issues/issue/24

Fixed the tests of preliminary and default model ids.
OPEN - task 24: Default extrinsic ID for objects with indexed features
or indexed classes 
http://github.com/markus1978/emf-fragments/issues/issue/24

Lots of refactoring, since we are using intrinsic id (only refered to as
id by now) instead of the former extrinsic id concept.
Added some tests.
Some bugfixes.
Issue 24 is fixed now.