Implement Authorization based on team association and current selection

[mediafinger]

Implement Team-based Authorization

• use the actionpolicy gem
• authorize all endpoints depending on which current_team the current_user has selected
• only being a member of team does not authorize
• the current_user has to select one of the teams they are a member of as current_team
• some actions only authorize current_members that have a required role (e.g. owner)
• other actions might be free to access to any logged-in user
• some actions might be free to access to anyone (guest user)
• users to not belong to teams - but pictures (and most other objects) should

[mediafinger]

Closed by:

• https://github.com/mediafinger/yournaling/pull/23