Rainlendar 2.8.1

- The time offset for the initial calendar wasn't initialized so if could contain a random value.
- Creating events with the quick add near the end of the month sometimes caused invalid dates.
- Deleting events from Lua script could cause a crash.
- Transferring the backup files between different computers works better now.
- Possibility to add custom audio as an alarm is now disabled for calendars which don't support it.
- For performance reasons the alarm window will disable automatic updating if it containse more than 10 visible alarms.
- Time offset now adjusts the weekday correctly for the weekly recurring events and tasks.