Cache Clearer incorrect implementation for multiple sensors

[phil0stine]

In cached_clearer.h update function, offset_from_costmap_x_ and offset_from_costmap_y_ are used to translate cache-raytraced cells to costmap cells. The values (and the clearing cache) are implicitly centered around the measuring sensor, but raytraceFreeSpace includes data from various sensors, so a single cache centered at a single point is not correct.

A solution to this (one cache per sensor) is included as the last commit in the more general pull request