Add support for configuration settings for Sensors.

[bmalhigh]

Support sensor configurations via AirSim JSON settings.

Validated on Windows and Ubuntu.

1. The list of sensors enabled on a vehicle (multirotor or a car) can be controlled via the settings.
2. Supports a default sensor list.
3. Allows for sensor specific settings to be configured via JSON (currently used for Lidar).

Example of a default sensor-list specified in settings.json:

"DefaultSensors": {
	"Barometer": {
		"SensorType": 1,
                "Enabled" : true
	},
	"Gps": {
		 "SensorType": 1,
		 "Enabled" : true
        },
	"Lidar1": { 
		 "SensorType": 6,
		 "Enabled" : true,
		 "NumberOfChannels": 16,
		 "PointsPerSecond": 10000,
		 "X": 0, "Y": 0, "Z": -1,
		 "DrawDebugPoints": true
	  },
	 "Lidar2": { 
		 "SensorType": 6,
		 "Enabled" : false,
		 "NumberOfChannels": 4,
		 "PointsPerSecond": 10000,
		 "X": 0, "Y": 0, "Z": -1,
		 "DrawDebugPoints": true
	  }
},

Example of a vehicle specific sensor-list specified in settings.json:

"Vehicles": {

	"Drone1": {
		"VehicleType": "simpleflight",
		"AutoCreate": true,
		
		"Sensors": {
			"MyLidar1": { 
			       "SensorType": 6,
			       "Enabled" : true,
			       "NumberOfChannels": 16,
			       "PointsPerSecond": 10000,
			        "X": 0, "Y": 0, "Z": -1,
			        "DrawDebugPoints": true
			},
			"MyLidar2": { 
			        "SensorType": 6,
			        "Enabled" : true,
			        "NumberOfChannels": 4,
			        "PointsPerSecond": 10000,
			        "X": 0, "Y": 0, "Z": -1,
			        "DrawDebugPoints": true
			}
		}
 }