Add Line-of-Site to Physics Coodinator

[tylerferrara]

ROS NetSim currently uses a dummy physics_coordinator which doesn't throttle robots in accordance with their models.
In order to change this, we must debug the gazebo_custom_server to allow line-of-site communication.
Additionally, need the ARGoS sim needs to integrate with the physics coordinator swell.

• Add Gazebo line-of-site
• Add ARGoS line-of-site
• Test line-of-site for travis on BOTH physics engines

This issue blocks #5

[tylerferrara]

@nikopoulospet Where can I find your work for ARGoS line of site?

[nikopoulospet]

Argos Bridge repo, should be a submodule in the main nest repo