Reimplement crop date range capability (#718)

* add placeholder functions for date range cropping

* refine crop_date_range function. Need to figure out how to pass calendar from subset df

* continue reworking crop_date_range

* revert changes to check_group_daterange, and add check that input files overlap start and end times
add option aggregate=false to to_dataset_dict call
look into replaceing check_time_bounds with crop date range call before the xarray merge

* reorder crop_date_range call
add calls to parse xr time coord and define start and end times for dataset

* finalize logic in crop_date_range

* remove start_time and end_time from, and add time_range column to catalog generated by define_pp_catalog_assets

* replace start_time and end_time entries with time_range entries populated from information in processed xarray dataset in write_pp_catalog

* remove unused dask import from preprocessor

* replace hard coded time dimension name with var.T.name in call to xarray concatenate

* add check_time_bounds call back to query and fix definitions for modified start and end points so that they use the dataset information

* fix hour, min, sec defs in crop_date_range for new start and end times

* strip non-numeric chars from strings passed to _coerce_to_datetime

* add logic to define start and end points for situation where desired date range is contained by xarray dataset to crop_date_range