add skew-t

similar to https://ensemble.ucar.edu/sounding.php?d=2017100500 where one can click on the map to get the forecasted skew-t for that location. Probably easiest to use https://github.com/rsobash/d3-skewt, send the data via bokeh, and have a bokeh javascript callback to update the d3 data.