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* Added signal to catch version deletion and make sure nb_version in versioned models is coherent
* Added test for this
* Made sure pending moderation data (that was automatic) and versions are deleted when a model is deleted.
* Added test for this.

Fixes #84

* Added new BaseModel /serializer/viewsets
* Change names of abstract models/serializers/viewsets
* Folder structure changed in tha backend
* Added some backend test
* Corrected bug related to moderation on non versionned modeles
* Corrected bug related to no post permissions
* Updated doc accordingly

Fixes #91