Provide easier way to unsubscribe from multiple groups
Related commit: 1c739d97
Current behaviour: Newcomers have to unsubscribe from groups they are uninterested in individually.
Expected behaviour: It should be easier to unsubscribe.
- Ask users which group they want to subscribe to when they signup
- Don't subscribe new users to all groups, maybe ~3-4 popular groups
- Bring back the subscribe/unsubscribe button on groups page