Makes VoxelLayer keep track of what costmap cells are updated
Adds ExtendedVoxelLayer which adds the option to update with differential overwrite instead of bounding box
Adds publishing of which cells are cleared by the ExtendedVoxelLayer
Added type info output about costmap plugins to ROS_INFO
Merge pull request #10 from AlexReimann/costmap_update_update

Adding ExtendedVoxelLayer