It knows better than we do about its own dependencies.  Let it control them.

It is better than what we have here and duplicating it is sad.  ZKAPAuthorizer
also has much tighter binding to Tahoe-LAFS version than anything in this
repository so it makes sense to let it dictate that detail.

Also bump the version being used.  This will be important in a minute.

Also open the firewall!  Yea.  That is a pretty important thing.

This results in less repetition, less abstraction leakage, and provides more
power to the private-storage module (by exposing meaningful values instead of
Tahoe-LAFS config strings).

Also, comments.