Fetch hourly lists from Onionoo with relay status

From the Tor Weather (Rewrite) wiki page wiki:doc/weather-in-2014:

Once per hour, download a list from Onionoo that contains relays that have
been running in the last week. Check if there are any relays that have
been offline for long enough to notify a subscribed user. Send out emails. 

For now, we will concentrate on this subset:

• query Onionoo for a list of relays containing the appropriate information
• keep this query as lightweight as possible
• considering the current weather-design, work out which relays qualify for a 'NodeDown' event
• output identifier (this could be the contact data directly from the relay, or, to patch this into current weather sometime, the fingerprint)
• do this hourly

Email notifications will be left out for this initial phase.

Trac:
Username: baumanno