Fix NumberFormatException in AlarmReceiver.

+ Application crashed when alarm was due for a lecture. Bundle keys for
  add and delete alarm actions must be identical.
+ Bug was introduced here: 62e2890750d36b8988440d496b06d632590d6551
Fix crash when returning from alarm settings without the schedule downloaded.

+ This happens when there is no network connection to download the XML.
Merge pull request #33 from johnjohndoe/bugfix/alarmreceiver-numberformatexception

Fix NumberFormatException in AlarmReceiver.
Merge pull request #34 from johnjohndoe/bugfix/access-lecture-list-when-not-connected

Fix crash when returning from alarm settings without the schedule downloaded.