Combine registration and group

[sumanthratna]

Current Process

1. create a register link (with random ID)
2. send register link to campaign
3. campaign creates account using register link
4. I add name and email manually to the group_references table in the database

Proposed Process

1. create a group in the admin panel, providing group ID, name, and email (should allow arbitrary number of admin accounts per group)
2. all admin users in the group receive an email containing login instructions, link to group form, etc