DNN-26716 Profile properties not filled in when registering with social media authentication providers

The OAuth authentication providers (Twitter, Live, Google, Facebook) try to fill in profile properties but fail on a lot of them, due to a bad inheritance scheme.

This pull request included tests which show the issue (in a new project `DotNetNuke.Tests.AuthenticationProviders`), and updates to the `UserData` classes to make those tests pass.

This pull request addresses the issue raised in [DNN-26716](http://support.dotnetnuke.com/project/DNN/2/item/26716)