Now removes output after successful run

After a successful run, the program will clear txtOutput so user's don't
accidently overwrite their previous output.
Convert button now becomes disabled while running
Added a function to obtain file sizes
Changed the default file names on the file dialogs
Changed the file size function to output as a double

This was done so calculating differences would be easy. It was useless to
convert the return to a String, then convert it back to a double to do math.
Now verifies the file size after encoding

After a successful encoding process, the program will verify the file size
and make recommendations if it is larger than what the user specified.