[bugfix] Make sure to clear previous output to indicate that processing is occuring
[bugfix] Make sure to catch exceptions and display at least an error in the output window, otherwise if the user is not running the app from a terminal they may not see any error - just blank output!
[bugfix] Suspend Validate button when validating
[feature] Show wait cursor when validating
[feature] Remember last used file paths between application invocations
[bugfix] Be sure to close the Metadata file and Schema file when we are finished with them