Consider keeping data from the last 30 days instead of 5 last days

I think torflow keeps measurements from the last 30 days (have to find the code line again). That could explain why sbws is still voting on less relays than torflow. However that would make the sbws still slower having to load 6 times more files an ~500 more relays' json data. The patch is simple, maybe we can try it in longclaw for a week, maybe without even merging to maint-1.1 branch.