Enable Tor Browser users to become "easy to be run" Tor Exit relay

This ticket is to enable TorBrowser users to become "easy to be run" Tor Exit relay.

The end-user workflow should be no more than:

click "Contribute to Tor network"
then picking the destination they do want to allow among the top 30 traffic destinations
Confirm

The destinations are measured by ticket #18268 (moved)

The end-user must be shown a visual feedback and easy-to-be-understood statistics that enable to "perceive" and "see" that traffic is flowing.

An indication on "How many other users has been helped stay safe" would be the best gratification for and end-user to leave TorBrowser open in pushing out non-abuse-generating Tor exit traffic "helping other users".

That would require also implementation of ticket #18267 (moved) to be able to setup "Autonomous System Aware Exit Policy", enabling the configuration of a destinations as "Google" .

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information