Feature/team management

Addding some stuff for team management:
- manage, update, edit actions for team.
- adding invitation model and controller. Really simple model: the leader send invitations to free players, the invitee can accept or decline from his profile page.

And some tests \o/

Tell me if you see any security or coherence issue (players who already have a team should not able to accept invites, and so on...)

Of course take your time to review :watch: ( good amount of code :smiley: )