Refactor/remove proxy-pair state machine in webextension
The snowflake badge and webextension code is heavily based off of flash proxy, but the proxy pair state machine, which used attributes such as "running" and "active" doesn't map as nicely to the webrtc context. It would be nice to refactor this to be simpler, more closely match our understanding of the webrtc state machine and be easier to maintain. This might mean removing these attributes entirely and using the existence of proxy pairs to indicate if there are any open or running connections (see https://trac.torproject.org/projects/tor/ticket/31100#comment:23).