Sponsor request fulfilled

https://osraav.atlassian.net/browse/OSRA-87

Implement request_fulfilled field in sponsor:-
- create migration
- added field in index, show, edit 
- field not show in create
- model validations implemented

OSRA-87 OSRA-88 OSRA89 OSRA-90 #code-review

Just to show that I really did review the code: this can be `expect(sponsor.reload.request_fulfilled?)`.
Also, there is an extra space within the parens and no spaces inside the curly braces on L34.
OK, done nitpicking