Support output in feet for /getelevation and /getheightprofile in the elevation service

[raynerhoward]

Probably more of an enhancement than an issue . . .

I'd like to see elevation values in feet in the MapInfoTooltip (when you right-click on the map) and also view the height profile in feet (both distance and elevation values). The DEMs (GeoTIFFs) I'm using are in US StatePlane with coordinates in feet. Elevation (pixel) values as per band.GetUnitType() are in 'US survey foot'. Would be great if this could be configured in the python script, config.json and/or the service config file.