Cope with other events coming in

The only key which seems to be guarunteed to exist is the type of
event, so check that first. All the events we can handle have
project and revision in the expected places.

Change-Id: I390f00e578e9b42bc2d9c41da37548b555103be8
Expose more than just the user's emails

We need to be able to inject their names into the email if asked.

Change-Id: Ibec4c22ec157e6a635a8fafc73d24bbf68f726a7
Add a GroupMailer which wraps sending a template

This does the work of looking up the group members and then sending
the emails.

Change-Id: I492f7d28802331e76e34c47eb0101262a34bee09
Update libfritter to pick up latest changes

Change-Id: Icc3b9b7724f5d0f996cdf81b75e9948f3da6ba95
Implement actually sending the emails

Change-Id: I01a2e0c37f124db9f96e57fb59fe208b37715089