MT#6731 Remove "back" param from form if posted.

Somehow this sneaked in from somewhere and so far only happens with
resellers, so make sure to just clear it if a form got posted.
MT#6687 Use transaction when cloning set.
Subscriber profile management. WIP.
MT#6693 Properly handle sub profile attributes.

Store selected attributes.
Let them be edited.
Correctly clone attributes.
MT#6693 Assign profiles to subscribers - WIP.

TODO:
- Subadmins must not see a "Create" button in profile selection
- Can sub(admins) unset a profile? What's the default?
MT#6693 Basic pref filter based on subs profiles.
MT#6693 Introduce profile catalogs.

Profiles are grouped into catalogs, so a subscriber should get a
catalog assigned, and from there he can choose his own profile.
MT#6693 Align subs profile CRUD to catalog schema.
MT#6693 Rename profile categories to profile sets.
MT#6693 Let subadmins edit subscriber profile.
MT#6693 Let admin/reseller clear subs profiles
MT#6693 Filter call-forwards for subs profiles.
MT#6693 Let subscriber edit reminder.
MT#6693 Add separate form for subadmin pbx flow.
MT#6693 Remove reseller "back" param workaround.
MT#6693 Fix profile(set) editing of pbx subs.
MT#6693 Rework PBX subscriber/group handling.
MT#6693 More subscriber editing rework.

- Update base cli of extensions on pbx admin primary number change.
- Use proper forms (hopefully) for editing various pbx subscriber types.
MT#6693 Fix PBX group editing.
MT#6693 Show extension vs number for customer subs