add gem_gazebo interface with control commands to gazebo

Author: harishkumarbalaji

GEMstack/knowledge/defaults/current.yaml

@@ -12,8 +12,8 @@ control:
         brake_amount : 0.5
         brake_speed : 2.0
     pure_pursuit:
-        lookahead: 2.0
-        lookahead_scale: 3.0
+        lookahead: 4.0
+        lookahead_scale: 1.0
         crosstrack_gain: 1.0
         desired_speed: trajectory
     longitudinal_control: