New roles for event management

[ctizen]

• Owner role: equivalent to administrator, but can't be revoked by anyone. Owner role can be transferred explicitly to another user (with confirmation).
• Manager role: can only add new players to the event and cancel hands or games when possible. Manager can't remove players from event, assign other managers or administrators or change event settings.
• Consider adding non-playing administrators (now one can add player, make them an administrator, then remove, but it's a workaround)

[ctizen]

TBD in new management service