Rename, link to demos and tutorial for Kobuki messaging channels

[stonier]

• remove the ros_ prefix for sigslot channels ros_debug, ros_info ros_warn and ros_error →
• link to the remaining demo programs (tools and simple_loop_control already covered) →
• demos that exemplify their usage → [logging] removed ros_ prefixes, internalised logging #40
• demo documentation → [apps] logging and raw data stream listener kobuki_documentation#34
• update kobuki_node to refer to the new names and set the log_level to NONE → [slots] ros_ prefixes dropped in kobuki_core, updated here kobuki_ros#16