Purge RPC (#268)

* purge removes cert files

* reeneter setup mode after purge

* use single channel

* simplify select in run_gateway_loop

* cargo fmt, comments

* update protos

* fix log

* cargo update

* use oneshot channel

* on purge drop the interface and cleanup firewall rules

* more state cleanup when purging

* log formatting tweaks

Author: j-chmielewski