Table sorting and filtering for semester result overview

This adds data tables (http://datatables.net/) to the semester result overview and fixes #48.
- Filter by name of course/type/...
- Sort by course/type/...
- Sorting the last column (voters) currently sorts by the voter/participant ratio
- Works in English and German
- Users without JS simply see the old table

![datatables](https://cloud.githubusercontent.com/assets/2820802/3718185/f485ca3c-1632-11e4-8b5f-ba081ad56ac4.png)