R1:8f2c426ff2c3

Fix OAuth Client Authorization bugs

Summary: ajtrichards reported an error creating a brand new authorization. fixed that and generally made this flow work well

Test Plan:
- created a fresh test client
-- noted "new=<PHID>" with appropriate highlighting
- visited http://phabricator.dev/oauthserver/auth/?client_id=PHID-OASC-jwgdrqdpzomtxyg3q3yf&response_type=code&scope=offline_access
-- clicked "cancel", verified result
-- clicked "approve", verfied result
- visited http://phabricator.