Port the web application from flask-fas-openid to Flask-OpenID

This allows us to support more openid server than just FAS-OpenID and thus
allowing people outside the community to get notifications.
Add a login template
Add a configuration key for the URL of the Fedora OpenID server
Add a generic login place as well as a direct Fedora login

The generic login can be used by anyone to use their own openid server while
the Fedora login allows to directly login against FAS w/o having to precise an
openid endpoint.
Add configuration keys to allow turning on/off easy access to openid servers
Adjust the main login links to the settings in the configuration
Provide easy login to main openid servers (google and yahoo)
Use fullname when no nickname are provided by the openid server and fix typo
Set the list of admins in the configuration file
Add the google logo
Add the yahoo logo
Use the google and yahoo logo into the login page for their respective openid
Require flask-openid.
Switch to use openid as identifer rather than the nickname

- This allows better support of other OpenID providers than FAS
- Usernames are only used to build the URLs and check the admins
- Save the email and the openid url in the database
Simplifies the openid URLs and catch exception if we two emails identical

The two emails problem could raise if someone has 2 openid providers providing
authentification for the same email (ie: FAS and it's own openid provider?)
Use the full openid_url for libravatar
Use the user's email in the page rather than it's openid identifier
Remove old print
Replace username by openid since it is what it is
Remove the email field from the User table and the application