Support non-standard parameters to authorization URLs.

Some OAuth implementations offer proprietary features through non-standard authorization parameters.

LinkedIn, for example, supports an OAuth2-like "scope" parameter even though LinkedIn's OAuth implementation is version 1.0a. Without being able to specify a scope, it is not possible to fetch certain data for a user...the user's email address, for instance.

Spring Social should support non-standard authorization parameters at authorization/provider-authentication time to allow for provider-specific extensions to the OAuth authorization protocol.