chg: bwfile: Count only recent days for `recent` Keys
which are 5 days by default, instead of the oldest days, which are 28 days. Also remove old Relays at the time of generating the BwFile instead of when a new one is created, so that in case the scanner wasn't run in several days, they aren't included and there aren't too many when the scanner is run again.
Closes #118 (closed)