[#1429] Pass came_from to login handler after creating a user

Otherwise you lose the language setting for the UI. I'm not entirely
sure but that may involve two redirects.
[#1429] PEP8 fixes
[#1449] Fix extras deletion

The custom-fields module was actually disabling the fields when clicking
the delete extra cross button. This prevented the key and value from
being sent, which caused a validation error.
We now change only the class to make it look disabled, which should be
good enough.
[#1449] Remove unneeded tests