Dashboard with all activity happening in your teams

- [x] activity model
- [x] track helper for application controller
- [x] track team events (:create, :update, :transfer, :destroy): "#{responsible} created/updated/destroyed team #{subject}"; "#{responsible} transferred team #{subject} ownership to #{target}"
- [x] track mate events (:join, :leave, :kick): "#{responsible} joined/leave team #{subject}"; "#{responsible} kicked #{target} from team #{subject}"
- [x] track skill events (:create, :update, :destroy): "#{responsible} added/updated/removed skill #{subject} for #{target} from team #{target.team}"
- [x] dashboard view renders all activity related to teams where user member is mate
- [x] activity is stored only for 2 days