Create a userInfoGET endpoint in OAuth2

[porcellus]

• it should be exposed by the OAuth2 recipe
• we want it to be available using an oauth2 access token (if it doesn't exists by the time you start, you can add a stub function for validateOAuth2AccessToken
• it should have a related buildUserInfo in the RecipeInterface (a stub for this has been added, but feel free to modify it)
• other recipes should be able to add their own "build" functions. check addClaimFromOtherRecipe
• the API logic looks roughly like this:

1. validate the incoming access token
2. build the default user info in an overrideable buildUserInfo function:
3. create the basic user info (email, phone number, userid, etc) based on the scopes
4. call the functions set by other recipes passing the scopes, access token and userId to them and merging the result into the existing user info object (you can add params if you think something else is necessary)
5. return the user info object that we got back from buildUserInfo