Create default command-line arguments and make --set_file optional

[KKhaghani]

Title. The first two command-line arguments can easily be given relative paths as their default arguments. As for --set_file, the only set file currently relevant for TFTInterpreter is gather_data/resources/set6_classes.txt. This might as well be a hard-coded constant at the top of the program; at the very least this third command-line argument should be made optional.