check index of Q series to allow for datetime index

[hwreeves-USGS]

Allowing the user to send a series of pumping with a datetime index might be useful.

Testing the type of index and converting to integer days would help simplify the generation of the series for the user and eliminate a step in their process - see the example notebook on the Well Class for the current process.

[mnfienen]

@hwreeves-USGS - if I recall this correctly, this just means we need to make a little function to map datetime-index-referenced pumping to sequential days and then run it right? I think this is a pretty light effort