Custom emails [PD-623]

There's no direct link to the 'edit your domains' page yet. I figured I'd wait until David was done with the UI changes to mess with that.

All tests pass.
There are one or two functions that I can think of off the top of my head that are used for admin-y stuff that might make sense to move if we really want to, but I'd say a solid 95% of that file search related.