Compatibility with ActionBarSherlock 4.3.0

ActionBarSherlock 4.3.0 removed dialog themes, including the Sherlock Light
Dialog theme which was being referenced in BlackboardGradesFragment. The
reference to the dialog theme was removed.
Migrated cache scheduler feature to new version

Updated the 1.91 cache scheduler version to the newest version at HEAD. Also
made a few minor changes from the previous version.
Fixed crash on schedule caching preference first-time enable

Really odd mistake on my part when I originally wrote the schedule database:
createDatabase() was catching an IOException and throwing back an Error. Not
really sure why I thought to do that, but it was triggering a crash and only
seemed to happen on the first time the schedule caching preference was enabled.