Saving intermediate camera images 

Added functionality to save camera images (rgb & depth) acquired at intermediate positions during a sweep to disk, as well as logging the TF position of the Depth camera and the rgb camera at each position along with the camera parameters in the sweep xml file. 

This information is useful for registration of individual point clouds acquired during a sweep, estimating motion in the scene at a particular sweep position, estimating a per pixel noise model as well as  rgb <-> depth camera calibration (intrinsic and extrinsic). 

Loading of the new data from the xml as well as the saved images is also supported by the metaroom_xml_parser (standalone parser for using the sweep data). 
This applies to all the changes in this file