Integrate Full Calendar into the UI

Integrate [fullcalendar.io](http://fullcalendar.io) into the UI

- Calendar shown in the main content container
- Add and Remove events through the sidebar (not hooked up to REST endpoints)
- Month, week and list view
- Design implementation according to latest wireframes and component PDF
- Fixed the position of the sidebar and header

TODO:
- Academic week number https://github.com/CUL-DigitalServices/grasshopper-ui/issues/31
- Changing terms https://github.com/CUL-DigitalServices/grasshopper-ui/issues/31
- Hook into REST endpoints when they're finished
- Popover with detailed information on hover of an event https://github.com/CUL-DigitalServices/grasshopper-ui/issues/30
- Sort out print view https://github.com/CUL-DigitalServices/grasshopper-ui/issues/29
Good call, makes it a bit cleaner by avoiding the [0] as well.