Use depth confidence to weight PnPRansac and/or local BA


See http://official-rtab-map-forum.206.s1.nabble.com/Bunlder-export-what-poses-tp11037p11229.html and http://official-rtab-map-forum.206.s1.nabble.com/Bunlder-export-what-poses-tp11037p11230.html

The general idea is to put more weight on features with high depth confidence or more noise/variance on features with low confidence. 