publishes range_max for invalid readings

This is useful for clearing in costmap_2d
Merge pull request #104 from efernandez/range_max

Publish range_max for invalid readings
Revert "Publish range_max for invalid readings"
Merge pull request #105 from ros-perception/revert-104-range_max

Revert "Publish range_max for invalid readings"
exports DepthTraits
exports depth_conversions (convert for xyz PC)