[strands_movebase] Don't add obstacles at edge of laser's FOV

This pull request adds a new node, `remove_edges_laser` that removes a small angle at the beginning and end of the laser scan. This new scan is then used to add obstacles in the costmap while the old, full, scan is used for clearing them. This should solve https://github.com/strands-project/strands_movebase/issues/25 .

Since I am able to try this out on Rosie atm (going on 48 hours now=P) and we are performing a marathon, I would encourage those that think that this affects the performance of their robot's navigation to try it before we merge. @BFALacerda @lucasb-eyer