[#41156935] Init commit for labellable persistence

Needs to clean the concept about labellable
[#41156935] change contents subclass to label

Still work in progress. The spec fails.
[#41156935] still draft ver. of labellable persistence
[#41156935] Improved labellable persistence

TODO: Fix Label's Model instance
[fixes #41156935] Add label persistence

All specs passes.
Merge pull request #66 from maxigit/41156935_add_labels_persistence

41156935 add labels persistence