DETECT_GRASS Snowpack filter

The DETECT_GRASS filter (enabled in the [SnowpackAdvanced] section) determines if the measured snow height is due to growing grass or to real snow. Although it has proven very useful, a case has been found where it totally messes up the snow height: when using research mode, without erosion nor redistribution (but still 5 slopes), for the WFJ2 station in November 2018. Turning OFF this filter solves the mismatch between measured and simulated snow heights.