Rgbd fixes

[akgoins]

@drchrislewis, please review. This includes some code cleanup but primarily fixes depth_calibration.cpp to correctly handle special cases (NaN's in the point cloud, large stddev in target pose calculation, etc.).

[jdlangs]

@akgoins, it would be nice not to force a dependency of openni_camera on all users of this repository, especially if they have no need for the rgbd_depth_correction package. Will it be alright to change this back to reading the config file from a parameter instead of directly calling for the serial number?

[akgoins]

Yes, it would be fine to go back to a parameter. I did this to make the cameras hot swappable, but using a parameter would make it easier to use with other cameras which don't have a service for getting the serial number.