require invites webapp/bitmask

2 different settings define whether invites are required or not, webapp.invite_required and provider.enrollment_policy. For example when this are like this:

webapp.json     "invite_required": false
provider.json   "enrollment_policy": "invite"

You can register through the webapp without invite, but not through Bitmask.

webapp.json     "invite_required": true
provider.json   "enrollment_policy": "closed"

The signup button doesn't appear, the signup page redirects you to the frontpage: good

webapp.json     "invite_required": true
provider.json   "enrollment_policy": "open"

You can't register without invite through bitmask, because you get the error This is not a valid codeThere is no field to fill out an invite code.Signup through webapp works, with invite code.

Related to #8842 (closed)