Update for WB-765: Upload Scene File to BALSA Dialog Updates: When finding the...

Update for WB-765: Upload Scene File to BALSA Dialog Updates: When finding the base path for a scene file, verify that each data file in the scene exists.  When the user presses with the "Zip" or "Upload" buttons on the Scene Dialog, find the base path and test for missing data files.  If there are missing data files, display a warning dialog listing the missing data files and allow the user to continue or cancel.