Getting ready for RailsGirls Summer of Code 2014

- brings back the features present on http://2013.teams.railsgirlssummerofcode.org/
- updates the help-page (#99)
- adds the `Event`-Model (#102)
- let's assign an event to a team
- adds [coveralls](https://coveralls.io/r/rails-girls-summer-of-code/rgsoc-teams) (since we should improve coverage a little bit. :))

Still missing:
 - [ ] Participating filter for the users overview (see #101)

Blog post aggregation still works as last year, we need to enable the rake task as a cronjob again.