726 request emails

Resolves #726 
I think we can tweak the language here a bit, how about something like "You can pick up your [equipment_model] on or after [start_date] and should bring it back before [due_date].", more or less. I just think it should be a bit less of a command, e.g. "PICK UP YOUR EQUIPMENT ON THIS DATE [OR ELSE]" :-P