Bag of improvements

Sorry I haven't split these out into different pull requests. I've done three things here:
- changed printf's to ROS_INFO and fprintf(stderr..) to ROS_ERROR
- used the camera_info_manager to give usb_cam more standard handling of camera params. I copied the way things are done in https://github.com/ros-drivers/camera1394
    - this has the effect of changing the way params are loaded. instead of having a param called "K" for instance, there is a yaml file for the camera which has a member called "camera_matrix"
- added support for setting the framerate via a "framerate" parameter. defaults to 30fps