Updates to SWE Snodas maps

[lbross]

1. Add "mean" to the title for each month. Example: SNODAS Mean SWE, Nov 1st
2. New color scheme as suggested by Lexi. Colors for first 2 intervals are under discussion: 0: gray 0 - 0.5: white 0.5-7.5: light blue 7.5-15: medium blue 15-22.5: dark blue 22.5 - 30: purple 30-37.6: dark purple