Allow members to follow other members

This implements PT 46522139. Members should be able to follow other members with this patch.
Currently, when someone follows us we'll be getting both a message in our Inbox, and an email. The email uses app/views/notifier/notify.html.haml as a template, and this contains some of the extra text you mentioned above. Do you think that may be redundant? I'm gonna leave this alone for now, potentially something we could talk about the next time we meet.