Make UserClass editable by admin

[vincent-peugnet]

Re-use the userclass/id by adding a userclass/id/edit and a userclass/id/delete.

access would be controller by userClassVoter checking if user is admin.

edit

Should be the same form as add but with a few differences:

• The rank could only be set between next and previous userClass ranks.
• the submit button will be called "edit"

Delete

On delete, all the user will migrate to the next lower user class or then upper. It will be impossible to delete the last userClass standing.

[vincent-peugnet]

closed by https://github.com/vincent-peugnet/antilope/commit/2c83379db55468b26d12c4752c64ccb0bf803f45