Adresses #159 - Replaced backbone.fetch-cache with custom version.

The library will be switched back to the original version as soon as our customization is pulled into the repo.
Adresses #159 - Using prefillExpires in calendar / timetable.
Adresses #159 - Extracted cache defaults into utils.
Adresses #159 - Added caching for lectures.
Adresses #159 - Added caching for grades.