Resolve WB-696 Warning if NIFTI has both qform and sform invalid. A "file...

Resolve WB-696 Warning if NIFTI has both qform and sform invalid.  A "file warning message" (with methods to 'add' and 'get' warnings and the 'get' method will clear the file's warnings) has been added to the DataFile class.  At the end of VolumeFile::readFile, hasGoodSpatialInformation() is called and if it returns false, the 'add warning' method is called with a string indicating that both sform and qform are invalid.  After any type of file reading (load file, read spec file, show scene, etc.), all data files are queried for file read warnings.  If there are any file warnings, a dialog is displayed listing the file(s) and warnings(s).

Note: If the user requests loading of a Scene and a data file in the Scene is already in memory, the data file is NOT reloaded to save time.  In this case, no warning will be scene since the file remains in memory and is not read from disk.