Gridclim_dict for high gridded cell count

[jphuong]

Gridclim dict has a hardcoded threshold for performance reasons. Currently, if the mapping file gridded cell count is above 500, then the daily variable dataframes would be removed from the dictionary output.

We've had a discussion to incorporate this threshold limit as a gridclim_dict input parameter. Thus far, it would make sense to incorporate a default number to prevent slow performance from high virtual memory burden. A second concern is that without this threshold the resulting dictionary output is far too large for use (export or read-in) as it will be in the order of gigabytes.