Add Users

Added the ability for superusers and admins to add new users.

This functionality is not exposed through the UI yet (i.e. there are no
links to it).

Also fixed a bug with drop down labels, and table locking in the
membership form.
Add Organizations

Added the ability to add new organizations without going through the
membership application process.  This is exposed through the
"Administration" UI, since it is an admin-only function.

Fixed a bug with table locking in the membership application form.

Added a missing null check to the person controller.

Updated the organizations' users and organizations' payment info
templates so that they display a message rather than an empty table when
there are no results.
Add Users (UI)

Added links to the add users functionality throughout the UI.  Sitewide
admins get a link on the admin page and on every organization's page,
organization admins get it on their organization's page.

A few bugfixes:

Revamped the way login is handled, a 3xx is now sent to get rid of the
login=true query string, which eliminates some bug prone handling
related to that.

Added a null check to the person controller so that superusers with no
organization can't create more users.