Fix pagination of the fb_graph gem

The previous code used a whitelist approach to including params, but
that does not work with facebook's new paging param 'after'. It also
excludes parameters like 'include_deleted' and 'include_completed'.

This implementation excludes the only paramater that we don't want to
circulation, access_token, since that's provided by fb_graph.

Also, we would have liked to update the fb_graph-mock gem to have newer pagination examples, but did not because we don't know if facebook has completely eliminated all uses of the old params, and because we want to fix our code asap.