First stab at scripting function for VIIRS imagery [1594]

NOTE:  this code depends on [IDV pull request 84](https://github.com/Unidata/IDV/pull/84) so I'll leave this as a pull request for now.

I started a redmine page with usage instructions:

https://mcidasv.ssec.wisc.edu/projects/mcv/wiki/GetVIIRSImage

[1594]