Surface data bounds check not working properly in the GUI DEM download widget

[nwagenbrenner]

The behavior seems inconsistent between Linux and Windows. This may be an issue of installing the srtm bounds json file in the proper data location during the Windows installation. We should verify that things are working properly on Linux first and then look into why it's failing on Windows. It may be a simple fix of putting the needed bounds file(s) (I think it's just the SRTM json and gmted and LCP just use hard coded lat/lon bounds) in their proper location in the nsis installer. Relevant files:

NSIS Installer code: CMakeLists.txt
GUI widget bounds checking: WidgetDownloadDem.cpp
SRTM json bounds file: srtm_region.geojson