Update SkewT: correct hydrometeor integration, other user suggestions

[cshartsough]

The skewT diagram needs to change how the vertically integrated mixing ratios are calculated. Instead of summing the profile directly, it should vertically integrate based on the pressure levels. This should be similar to how the Precipitable Water field is computed.

Other suggestions:

• add the model name to the figure title
• add a scale factor to the CICE to move the profile into the same range as the other hydrometors (and add that factor to the legend)
• test the profile lines to see if they need to be turned off when moving to/from zero. try thinner lines and check with other sample profiles.
• correct the units in the legend to g/kg

[cshartsough]

These changes were implemented in PR 72 and PR 73, April 2021