Add support for acquiring OpenID claims when making a token request with a UserCredentials grant

[jcherniak]

No description provided.

[bshaffer]

Merry Christmas! This is a great pull request, thank you for your contribution! A few thoughts:

1. The tests are failing because issuer needs to be set on the server in order to use the IdToken storage in OpenId\GrantType\AuthorizationCodeTest.

2. This brings up the issue of backwards compatibility.Your changes will break those who are currently using use_openid_connect but have not set the issuer parameter. While it's unlikely someone would be doing this, it's unfortunately possible.
   Another issue is someone could update this dependency and now their token controller behaves differently than before (e.g. responding to the openid scope) without their knowledge. So it may be best to submit this to the 2.x branch and I can push to getting a new version out. We can also submit it to the master branch, but use a different config parameter, e.g. use_openid_connect_token_controller

3. Please add tests for the new functionality!

Thanks again, I'm excited to get this merged!