libgis: add ndwi colors, make population_dens a gradient

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@59137 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/gis/colors/ndwi

@@ -0,0 +1,6 @@
+-200 white
+-1.0000 white
+-0.2000 205:193:173
+ 0.0000 150:150:150
+ 1.0000 blue
+ 200 blue

lib/gis/colors/population_dens

@@ -1,11 +1,7 @@
 0 white
 1 255 218 164
-4 255 218 164
 5 255 186 90
-24 255 186 90
 25 205 129 32
-249 205 129 32
 250 139 64 16
-999 139 64 16
 1000 90 4 0
 1000000000 90 4 0