Our consolidate fees had a crash bug (and was pretty convoluted). This
makes it less convoluted and resolves the crash.
The only kinda meh thing is that we have to look up the most recent
timestamp data for the onchain fee entry separately, because of the way
SQL sums work.
Any file in this directory which is executable and whose name only
consists of alphanumeric characters, space, '.', '-' or '_' will be
automatically loaded when lightningd starts (unless suppressed with
commandline options).