Currently when admin add/remove/update custom fields, changes
are not reflected in user settings page, if settings tab
is already open. This might be rare case, but it looks like
an error when admin go to user settings page just after
updating custom fields in org settings.
Fix this by re-rendering custom fields in user settings
on custom_profile_fields event.
Now that we have support for displaying custom profile fields, this
adds administrator-level support for creating them.
Tweaked by tabbott to fix a few small bugs and clean up the commit message.
Fixes#1760.