Tweak some comments.
Convert navigation to be contained within a class.
Nav: rip all the service calls out to before init.
Tear A* out into its own function in corobot_common.
Tested the new nav code and found stupid errors.

Mostly imports and wrong variable names.
Add better comments to navigate().
Nav: remove sketchy graph hacking.

Instead, simply modify the neighbors function to check for nodes named
START or nodes in goal_zone, and return the appropriate neighbor list.
Merge pull request #10 from corobotics/max

Rewrite of the navigation node.