add onOriginChanged logic

[dorezyuk]

Hi guys,

I've added an additional function onOriginChanged.

The main idea behind this is to allow to implement layers/cosmaps which are not always rolling but also not entirely static (something in between). So the user can call LayeredCostmap::updateOrigin, if he wishes to move the costmap, but can treat it as static in the remaining time.

The concept fits also well in the current code base - allowing

1. unify the logic from ObstacleLayer and VoxelLayer
2. avoid redundant repainting in the StaticLayer (if the robot and thus the origin has not moved)

[dorezyuk]

@mikeferguson friendly ping