Add --group parameter to command line arguments

updated the config options to use the "--group" argument. a user can now
use the command line arguments in the following way:

program --group camera.fswebcam --use camera.webcam:WebCam.factory

or even

program --config_file file.conf --group camera.fswebcam --use
camera.webcam:WebCam.factory

This lets a user override the sections. The group refers to the section
name in a conf file.