107 Adds rtabmap rgbd visual odometry

[divyabudihal]

closes #107

These are the packages I compared (also described in the issue):

• svo: not meant for forward motion (ex. cars), too old, may not work with melodic, not maintained
• orb: does full slam with loop closure, too overkill for us
• lsd: old + does full slam
• dso: requires to much extra work
• kimera-vio: looks great but does not support mono
• RTAB-Map: has a dedicated node just for visual odom with rgbd
• ros_mono_vo: old and not maintained
• viso2_ros: it is old (kinetic), requires weird calibration file, works with monocular cameras

Chosen: RTAB-Map rgbd visual odometry: dedicated odom node, maintained, recent