Make extractTime in time_utils.f90 handle 2000-01-01T00:00 format

[wknoben]

Feature Requests

Description of feature
Time units in forcing files currently need to be in <units> since <reference time>, where <reference time> is YYYY-MM-DD hh:mm. Another common time standard is YYYY-MM-DDThh:mm (https://en.wikipedia.org/wiki/ISO_8601).

Description of the problem the feature addresses
This will make life slightly easier when working with datasets that use the alternative time format. Possibly mostly helpful to new users.

Will the proposed feature be backward compatible?
Yep.

Will the proposed feature change the science results of SUMMA?
No.