Load ICESat-2 and GEDI Data

[scottyhq]

• Sliderule is currently the best server option for getting subsets from arbitrary polygons https://slideruleearth.io
  • https://slideruleearth.io/web/rtd/user_guide/GEDI.html
  • https://slideruleearth.io/web/rtd/user_guide/ICESat-2.html
• It should also be possible to run client-side with https://github.com/SlideRuleEarth/h5coro

[scottyhq]

Added basic functionality for this, but will leave open until documentation is added.

priority is to bring in the standard DSM, DTM products from NEON/3DEP and doing the basic comparisons with ICESat-2, GEDI and WV stereo DSM