[#6692] Added support for OAuth2 Bearer Tokens

Support for RFC-6750: OAuth 2.0: Bearer Token Usage.
See http://self-issued.info/docs/draft-ietf-oauth-v2-bearer.html
for more information.  Doesn't support the Authenticate header.

Bearer tokens can only be generated manually by the user;
tokens generated via the existing OAuth negotation cannot be
used as bearer tokens.

Also consolidated the access token revocation form into the
consumer token generation page, and made it its own entry in
the auth menu.

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>