Implement passcrow.org monitoring

[BjarniRunar]

This code lives in passcrow.mon. Progress:

• Poll the stats endpoint to gather live info about running servers
• Measure the performance (response time) of the above polling
• Measure the availability (error rates) of the above polling
• Periodically put data in escrow, monitor success/failure rates
• Periodically initiate verification and retrieve data from escrow, monitor success/failure rates
• Use a JSON file from this repo to control which servers we monitor
• Display monitoring summary in tabular form on the website
• Publish monitoring summary as JSON on the website
• Document how to set up monitoring of your own servers using passcrow.mon

[BjarniRunar]

Progress has been made, https://passcrow.org/ is live!