Add documentation about the newly added configuration keys
Adjust the links to login according to the configuration of the application
Port nuancier to flask-openid fully

This change ports nuancier to use fully flask-openid adjusted to support openid-extension
see https://github.com/mitsuhiko/flask-openid/pull/23 for the appropriate changes

This allows us to construct the following model:
* Any person having an OpenID can login to submit a candidate
* Can only vote, people having a FAS account, having signed the CLA and being in one 
  more group than just the CLA
* Admin must also have a FAS account, have signed the CLA and be in the appropriate
  group