Invitations bug

Invited users are now associated with their respective organization immediately after a successful invite, rather than waiting for the user to accept the invite.

Previously, the "pending invite" system collected all the users with pending invites, and then looked up by email the organizations that they were invited for. Besides being convoluted, this caused problems when the invited user's email actually didn't match the organization it was invited for. This was happening when the organization's email had upper-case letters, which would be automatically downcased in the invited user's email (standard devise functionality). We're now avoiding all that madness by just directly associating the user with the organization during the invite process, and then the pending invite system gets what it needs by following the association.