Update to Nextcloud 12.0.5 - Released

The todos are sorted by priority.

Todos

• Mail App update to version 0.7.9  (done)
• Calendar App update to version 1.5.7 (done)
• Notes App update to version 2.3.2 (done)
• Collabora Addon to version 1.12.40 (done)
• Deck App Update to version 0.3.0 (done)
• Test of the migration for existing customers (done)
  
• Eat your own Dog-food. Update our own Clouds (done)
• Migration of all existing customers (done)