Fix bug that was showing raw HTML on admin pages
Simplify some logic with a notion of “sender”

The “sender” is the person responsible for sending the book; this is the
donor himself if the donor mode is send_books, or the fulfiller if the
donor mode is send_money.
Add fulfiller to “sent” event in admin view

Also tweak some related language
Simplify some admin views a bit
Add “paid” status in to some admin views