generated donation, interest, & transaction

the donation process. a donation is created by a donor (or user that's not logged in) and recipients can show interest. A coordinator will create a transaction between a donation and a recipient. basic views and forms.

issue #8 
Most of these should have "not null" constraints. Don't know how the Rails ORM differentiates between null string fields and blank strings though, so we might need to add additional constraints for string fields?