Authentication Manager: multi-role assignment#601

The /auth command could be improved by:

• Allowing users to select multiple roles
• Assigning all the configured roles when none is specified, as a configurable alternate behavior

This would be fairly useful for communities using multiple roles for staff members, such as one for permissions (Moderator) and another for hoisting (Staff) so they can be on-duty/off-duty or simply show as standard members for covert operations.

Available authentication methods would be defined by the highest-grade role, assignment can be done with a single API call, and roles with the same expiry time would also be removed together.