Rewrite to plugin structure for move_base

[SaxionLED]

Convert the skynav stack to be usable as a plugin for move_base, see:

http://wiki.ros.org/navigation/Tutorials/Writing%20A%20Global%20Path%20Planner%20As%20Plugin%20in%20ROS

Basically, there need to be two plugins:

• skynav_local_planner
• skynav_global_planner

Optionally also recovery strategies.