Added custom base height and water drop

elevstl usage is now ./elevstl <lat> <lng> <resolution> <filename> <waterdrop> <baseheight>, where 'waterdrop' is how far down the ocean should be dropped and baseheight is how heigh the base of the model is. Increasing water drop emphasizes oceanic coastlines and increasing baseheight make models stronger and easier to print.
Added water drop and base height inputs
Water drop and base height are passed to elevstl
Changed HGT file request name

This change should allow the bravo server to also access the regular server's HGT files without needing to duplicate them.