Publish zero velocity when reached to goal.

[spuetz]

Publish zero velocity when reached to goal. If the plugin is not publishing zero velocity to cmd_vel the robot will go one with the last command. This bug is in particular caused when setting the mbf_tolerance_check to true since the plugin will not publish zero velocity in most of the cases. Related to #32 and #70.

[howardcochran]

I request that this be made optional. Some controllers provide the ability to arrive at a goal at full speed as a feature. For example, TebLocalPlanner, when its free_goal_vel parameter set to true. This makes it possible to immediately give it a new goal so that it can go from goal to goal without stopping -- rolling through waypoints. If MBF hard-coded a zero twist, it would break this capability.

[spuetz]

Japp you're right!

[corot]

This got implemented with #166, right?