Admin: Create ability to e-mail all funders and requesters

[kylehg]

The ability to e-mail all the requesters or all the funders (or both) is something that staff (admin) users should have. At the every least, the ability to easily get all the e-mail addresses.

The actual backend call will be pretty trivial, it's a matter of jamming it into the admin somehow. If that proves extremely difficult, we can put it in its own view.