allow cfg_file to be passed as program arg

[hellkite500]

Allows the standalone BMI run to accept a configuration file arg from the command line.

After building with make you can execute ./run_bmi as before, and it will still look for the hard coded ./data/topmodel.run file.

You can also run ./run_bmi path/to/data/topmodel.run and it will use the provided configuration file instead.