AuthorizationOptions does not allow to query list of available policies

Due to the dictionary of policies being private there is currently no way to get all the available policies. Getting all the available policies is very useful when building Administration dashboards where you want to control and check what permissions a given user has.

Multiple users seem to have the same [requirement.](https://stackoverflow.com/questions/45014894/how-to-get-all-authorize-policies-that-i-added-in-the-startup-configureservices)