simplify oauth specs
Merge pull request #129 from 18F/oauth-helper

simplify OAuth specs
replace expect() with allow() in specs
refactor mailer code to make testing easier
fix specs
Merge pull request #130 from 18F/allow-expect

change usage of allow() to expect()
Show both closed and open carts (using common partial).

Tests!
Change user/index to show carts that the user is an approver for if there are no carts for which the user is a requester.
move link to carts to header rather than awkward sidebar thingie. Clean up some style duplication.