Update IWE and SWE ARDAC WMS style hooks

[cstephen]

Xref: https://github.com/ua-snap/ardac-explorer/issues/176

This PR updates the following WMS styles for the hydrology coverage:

• ardac_iwe_historical_era
• ardac_iwe_midcentury_era
• ardac_iwe_latecentury_era
• ardac_swe_historical_era
• ardac_swe_midcentury_era
• ardac_swe_latecentury_era

The WCPS query for each of these coverages has been updated to divide by 36 (3 decades * 12 months) instead of 3, and the colormaps have been updated with new value thresholds like so:

Ice Water Equivalent:

{"type":"intervals","colorTable":{"-9999":[0,0,0,0],"0":[0,0,0,0],"0.001":[158,202,225,255],"15000":[107,174,214,255],"30000":[66,146,198,255],"45000":[33,113,181,255],"60000":[8,69,148,255]}}

Snow Water Equivalent:

{"type":"intervals","colorTable":{"-9999":[0,0,0,0],"0":[0,0,0,0],"0":[158,202,225,255],"15":[107,174,214,255],"30":[66,146,198,255],"45":[33,113,181,255],"60":[8,69,148,255]}}