Added 'last transferred' property to WeekOverview

The last transferred property seems to indicate the last time sheet that has been sent to Afas. Days before this date cannot be edited anymore.
Added 'editable' property to DayOverview

Only days that are not transferred to Afas yet are editable.
More specific start date for DailyHoursListFragments

The start date is now set at exactly 0:00 in the morning of the Monday that starts the week.
Added UI affordance to display a day's "editable" status.

Fixes issue #1.
Disabled editing/creating entries for days that are already approved
Added functionality to request deleting time sheet entries
Added option for deleting time sheet entries in the editor action bar.

The menu option kicks off the DeleteEntryTask to perform the delete request. The option is only visible when not creating a new entry. After the request completes, the DayOverviewActivity gets a special result code to indicate the entry was deleted.

To keep the EditTimeSheetFragment as compact as possible, the SaveEntryTask was also moved out of the EditTimeSheetFragment.

Fixes issue #3.
Show busy indicator when saving or deleting in the editor activity