Aggregation and allocation in groups

[tobiasreischmann]

There is the wish to allocate choices to groups instead of users.
This makes huge changes in both the algorithm and the UI necessary.
Necessary features:

• Checkbox to enable group mode.
• Choose the groups, which are allowed to rate
• Prevent access by users, which are not in the respective groups
• Extend the algorithm to aggregate the ratings of the users per group (What happens with "0" ratings)
• Are the allocations still saved per user or per group?
• What happens to users, who switch groups while or after allocation/publication?

[abias]

I think this issue should be tackled together with #121