Set HTTP status code on error

Fixes TryGhost/Ghost#1055
Clean up test database after tests

Fixes #1064

- Updated grunt config for unit and functional tests to remove the test
database after each is run.
- Cleaned up a couple of issues with the functional tests that may have
been causing travis builds to fail randomly, including: the start page
is now `about:blank` instead of whatever page the last test suite left
off at, added some checks in the logout tests to ensure they're truly
independent of the other test suites.
Switching Travis button from private to public
Included NProgress in Production Grunt concat
fixes #1081: change contrib instructions to reflect #579
changes to support URI's without a scheme in config.js.
also removed "http:" from google fonts link to prevent a mixed content warning.
renamed LICENSE.txt to LICENSE
Merge branch 'master' of github.com:jgillich/Ghost