Added few db and symbol models with  serializers and views,
Added Sandbox Model. Added SandboxAddIn that adds automatic sandbox binding.
Moved all model classes to single file to avoid circular dependency. Temporary solution.
Made generic view add-in for classes that will be persisted as changes. Currently only for Namespace, Table and Column.
Added foreign key serializers (plain model serializer) for same classes.
Merge branch 'feature/dbmodel' into develop

Conflicts:
	fennec/restapi/dbmodel/models.py
	fennec/restapi/urls.py
	fennec/restapi/versioncontroll/models.py
	fennec/restapi/versioncontroll/views.py