Migration function to migrate data from official calendar to calendar+

[libasys]

1. Adding a migrate button to the settings dialog if calendar app is enabled
2. One click to migrate calendar data to calendar+
3. migrate existing sharees and port to calendar+ (milestone 8.2 or later)
4. Writing short migrate guide howto change .htaccess that current remote address for sync work

Want to back this issue? Post a bounty on it! We accept bounties via Bountysource.

[noci2012]

It's not just the calendar ->calendar+ db migration, all caldav links to the calendars need to be migrated as well, that may be troublesome depending the amount of calendars & users involved.
So the caldav front might need some attention as well.