Create e-agent that follows the controlled vehicle

[slivingston]

As a first demonstration of an adversarial agent that acts depending on the controller, create one that attempts to follow the path of the controlled vehicle.

[slivingston]

The first design should allow the e-agent to have knowledge of the exact pose of the controlled vehicle and thus be able to record the entire path history of it. It could also assume perfect information of its own pose. The second design should attempt the tracking using only onboard sensors.

[slivingston]

Code implementing this should be placed under the directory domains/dubins_traffic/e-agents/

[slivingston]

I had marked this issue as something to achieve as part of the second release of the dubins_traffic benchmark, but the existing wandering behavior e-agents/wander is sufficient. Thus I removed this issue from the milestone.