Changed the export functionality of ZipEntryManager to exporting the
validation reports of validation entries, instead of exporting carbon
copies of the input Zip files' CityGML files.

Adds alerts to inform the user of Exceptions/Errors that occurred while
parsing a ZIP file, instead of silently failing and closing the
openFileDialog window.

Use a BufferedInputStream for counting the bytes of a ZipEntry to reduce
the number of read operations on the hard drive.

Added the getDisplayName() function, which returns the filename without
the zipfile subpath prefix