Major rework of rc subsystem

Implement channels mapping calibration.
Store mapping in parameters.
Get rid of `controls` array and store control inputs in `controlRoll`, `controlPitch`, ... variables.
Move `channels` variable to rc.ino, channels are not involved when controled using mavlink.
'Neutral' values are renamed to 'zero' - more precise naming.
`controlsTime` is renamed to `controlTime`.
Use unsigned values for channels.
Make channel values in simulation more alike to real world: unsigned values in range [1000, 2000].
Send RC_CHANNELS_RAW instead of RC_CHANNELS_SCALED via mavlink
Don't send channels data via mavlink if rc is not used

gazebo/SBUS.h

@@ -18,6 +18,9 @@ public:
 	SBUSData data() {
 		SBUSData data;
 		joystickGet(data.ch);
+		for (int i = 0; i < 16; i++) {
+			data.ch[i] = map(data.ch[i], -32768, 32767, 1000, 2000); // convert to pulse width style
+		}
 		return data;
 	};
 };