integrate oauth2client and drop openid support

This is only a spike and not considered stable.
added tests for the new oauth2client integration
add .coverage to .gitignore
merge openid and oauthsupport

* if DJANGO_ADMIN_SSO_OAUTH_CLIENT_ID i not set it will use openid
* if DJANGO_ADMIN_SSO_OAUTH_CLIENT_ID is set it will use oauth
* when using openid a deprecation warning will be raised
* models OpenIDUser, Association and Nonce will only be imported if using
  openid
add python-openid to test requirements
import skipIf from django.utils unittest because it does not exist in python2.6
fix setup.py to include the newly created openid module
update readme
bump version to 1.0.0 pre