[Core] First working draft of multi OAuth provider implementation
[Core] Extend multi OAuth providers draft to be more elastic
[Core] Fix some issue in new OAuth provider implementation

Remove useless dependencies on EntityManager, add new UserOAuthInterface, extend UserInterface
[Core] Rename model from UserOauth into UserOAuth
[Core] OAuth providers fixed after comments, extend specs
[Core] Play with migration script for multi OAuth providers
[Core] Add missing unique index to Doctrine mapping of UserOAuth entity