Allow groupes in MyBoard

While we can create groups and use them to easily give access to boards, these same groups should be usable within MyBoard so the user could give access to his MyBoard.

That way, each time a user is added or removed from the group the access to the users' board is current. The users cannot modify these groups. Maybe the users could also have personal groups.

An example is having a projet managers group that will always have access to ressources MyBoards an have a view of their avaibility.

Thanks