ExitAuthority should be easier to run+resilient

The Exit Scanner should have a better wrapper, similar to that which we have for the Bw Authorities. This wrapper should check to see if a usable Tor is running, and if not launch it. It should check to see if a crashed soat run exists, and if so, use it to resume. It should also install the crontab for snakeinspector if it has not been installed.

Additionally, the cron.sh script should be saving the last time it ran successfully, and using that time to display new results, so that if snakeinspector begins crashing and then is fixed it will automatically mail results since the last successful run.