Add AMP Cache registration Method to Conjure

Adds an AMP Cache registration method to the Conjure client

This essentially just adds commandline flags to specify the AMP Cache URL and preferred STUN address to use for the registration method and then calls the appropriate station method.

To use ampcache as an alternative registration method, simply append the -ampcache flag to the ClientTransportPlugin line in your torrc file along with an ampcache address such as https://cdn.ampproject.org/

The work to implement this for the station is more involved