Move to using official epw2wea

 - Remove our embedded version
 - Look for NREL_ver.txt in radiance folder, prefer Radiance that has it
   over one that doesn't
 - Warn user if NREL_ver.txt is not found in the found Radiance
 - Use epw2wea that is found in the radiance folder
 - Double check that RAYPATH and PATH are being set.

@rpg777