Adds indexes to the OAuth2 related models.

Since the access token table grows extremely quickly, it is
imperative that we have proper indexes on this table. Additionally,
we should make sure that refresh tokens have indexes too.
Merge pull request #118 from waveaccounting/master

Adds indexes to the OAuth2 related models.
bumped version to 0.7.1
changelog
added ashchristopher to the authors file
Merge remote-tracking branch 'upstream/master' into openid-connect
Version changed to 0.8.1