Move several datetime_range, month_range to single location #128
Description
Leftover from #124:
I discovered a datetime_range in publicdb.py that is a bit different. Make it DRY: Move that datetime_range to utils.py and use it here. Rename the datetime_range from this branch (that spreads the remaining days over different intervals) to an appropriate name. And/or merge.
and:
About the datetime_range-type functions, I think we should move those to time_util.py.
I also have a monthrange in topaz that could be (with some modifications) placed along those..