Merge tag '8.5.0'

Release 8.5.0
Bump version number
Fix inconsistent passing of attendee and user instances.

Fixes #9
Fix deleting attendees causing an update to the to-be-deleted attendee price

Fixes #10
Make e-mail rendering a bit more robust
Merge branch 'release/8.5.1' into production
Merge tag '8.5.1'

Release 8.5.1
Improvements to event template
Remove event groups
Remove user groups
Bump version number
Merge branch 'release/8.6.0' into production
Merge tag '8.6.0'

Release 8.6.0
Allow required choice widgets without any choices to be "selected".
Version bump
Merge branch 'release/8.6.1' into production
Merge tag '8.6.1'

Bugfixes
Fix bug when editing profiles
Add policy to control validation of user location input
Remove package price from option groups