Voxel layer fix - to remove obstacles from the map after a timer

This is done by keeping track of time that a map index was updated last - as well as the indices that were updated at each timestep. We remove old obstacles from the map - if the observations are too old and the locations have not been updated after that. Enable this by adding 

clear_old: true
max_obstacle_persistance: 2.0 (time in seconds before obstacle points are purged)

Only works for non-rolling maps (such as the one used by the global planner). 

Also includes some small improvements to the updateOrigin functions that check if the new origin is the same origin and updates only if needed.