Util2d.plot() no longer masks inactive values

[jtwhite79]

The array plot helpers previously would mask inactive values as well as plot the inactive areas as black. Now the inactive array values are not being masked, which goofs up the color scale to make things look uniform if the values in the inactive areas are extreme (common practice)

[jlarsen-usgs]

@jtwhite79
I'll take a look at this and find a fix