Switched srcrepo to work with EMF-Fragments and fragmented models.
Add fragmentation to `SourceRepository_allCommits`.
Added fragmentations:
- SourceRepository and JavaModel in seperate fragments (childrem of
`root`)
- CompilationUnits as indexed containment
- Packages as fragmented containment
- Types ad indexed containment
- usagesInTypeAccess as indexed cross references
Adopted srcrepo to work with mongodb, which it successfully did in a
first test.
Some refactorings to the Java model/genmodel. 
Everything now works great with mongodb.
Added generated edit code that uses the new EMF-Fragments
`ItemProviderAdapter`.
Lots of changes to introduce EmfFrag and separate EmfFrag specific code from code working with regular EMF models.