Add capability to switch NEON sites to use PRISM forcing data

[ekluzek]

We've done research to show that switching out the precipitation from NEON sites for PRISM data (a 4km reanalysis) is useful. We'd like to make this an easy switch to make in CDEPS. So rather than using the NEON site date it would pull down the PRISM precipitation data for that site. But, there would be an XML config_component.xml variable that could be set, or a namelist or streams variable that could be set in user_nl_datm or user_nl_datm_streams.

#211 relates to this a bit, but this is about adding a particular stream in a more regular way that's easy to turn on.