[enhancement] Reduced checking frequency

[ninjaloose]

Might I suggest checking of trackers that have been offline for extended periods to be checked much less often to reduce the server load.
Something like tracker offline for:
3 months - check that tracker once per day
1 year - check once per week
longer - move to a "dead" list for people cleaning out trackers from their old torrents.
You could then weight those checks x times more than whatever they are now to equate to 24/checks per day or something for the uptime statistics