Add warning when domain is less than 100x100 grid points (any domain)

[HathewayWill]

Based on the best practices I think we should have the dx and dy flag red when the domain is less than 100x100 grid points.

So in that image 47 and 43 should be red

[JiriRichter]

Adding a link to the best practices for reference https://www2.mmm.ucar.edu/wrf/users/best_practices.html