umi_sats.py issues

[cfblaeb]

umi_sats.py is maybe useful, but a bit unfinished and unmentioned.
Its only used in the Makefile, which is also never mentioned nor used.

Should it be named umi_stats.py?
The command line arguments, -m, -M, are not required, but script will give an error if they are not provided because they have no default. (Line 220 and 221)
Function cluster_read_hist, line 198 and 199, draws a vertical line to indicate "Min cluster size" and "Max cluster size", but doesnt used the commandline provided values, but rather the "default" 20, 60.
Line 200 also, somewhat arbritrarily sets xlim to 200.

if -f is not set, then cluster_read_hist is never run