User form fixes - convert user edit screens to functional, use user context, update api to patch

[himdel]

Closes #106

Drop ActiveUserAPI, replace with UserAPI - also means real user info in profile
Fix PulpStatusAPI to use trailing slash.
Add pulp fields to UserType.
Add UserAPI.saveUser which deletes the fields we're not editing, and uses patch (update would unset the password whenever we weren't changing it).
Add updateUsername and updatePassword to UserContext, use when changing current user (to prevent logout on the next request).
Remove is_superuser remnants.
Update a couple of checks expecting to know current user id from context to use username.
Remove authentication provider from user form - pulp doesn't tell us.
Handle non_field_errors in user form.
Convert UserProfile, UserCreate and UserEdit to functional.
Restore save functionality in UserProfile.

Cc @lubosmj this should fix saving the user from user profile :)

[lubosmj]

It appears like this change has helped! Thanks!

In [2]: User.objects.first()
Out[2]: <User: admin>

In [3]: User.objects.first().last_name
Out[3]: 'Novak'