Refactor - Downloading of homework in its own class
Ad automatic updates preference
Implement offline cache
Implement automatic update
NOTE: Service isn't always started correctly yet
Implement fix for #14 in new homework downloading system
Fix date comparison bug
Let homework loading tasks actually run in seperate threads
Fix timing for automatic updates
Fix timing for restoring automatic update alarms after reboot
Merge branch 'master' into offline_cache

Conflicts:
	app/src/main/java/paarmann/physikprofil/HomeworkDetailActivity.java
Merge branch 'offline_cache'