Contibutions by Peter Rosenberg:

- WorkTimeTrackerActivity: new dialog to ask the user once if he/she wants to backup on Google servers + process dialog for backup/restore
- WorkTimeTrackerBackupManager: read backupEnabled pref key from key file
- DAO/TimerManager: add argument to createEvent() for restore operation
- WifiTracker: fix "stop tracking" on foreign wifi

git-svn-id: file:///home/svnroot-zephyrsoft/projects/trackworktime/trunk@538 f37aa4ac-6963-46a2-a1ff-558a307fa857