Start implementing new idea for contribs
Refactor contributions
Finish Contribution implementation
Complete contributable implementation

Must replace original date by creation_date
Be careful with updater / creator, as they are not set at the right time. Should be done on an after_initialize.
Remove original_date from Contribution
Stamp users on validation
Correct models and contollers tests
Starts restructuring contributions with PublicActivity
Fix models specs
Add owner on Contributable and fix abilities
Fix controllers tests
Fix contributions request tests
Fix imports regressions
Complete basic approbation screen
Add adapted flashes on albums/artists saves/contributions