Makes RF2 sending and receiving work for ESP8266 with added support for group bit and dimming (#113)

* Made rf2 sending and receiving work

With code from https://github.com/1technophile/OpenMQTTGateway/pull/109
plus some other fixes.

* Added support for group bit

Added support for sending and receiving group bit

* Group bit and MQTT retransmitting

Added support for sending and receiving group bit.
Made the gateway transmit the new state of a RF2 switch to the MQTT state topic when it receives a MQTT command to control that switch.

* Removed hard coded RF2 code length

* Added support for dimming to RF2

Verified to work with Nexa WMR-250 dimmer.

* Minor cleanup

OpenMQTTGateway.ino

@@ -173,6 +173,9 @@ void setup()
   #ifdef ZgatewayRF
     setupRF();
   #endif
+  #ifdef ZgatewayRF2
+    setupRF2();
+  #endif
   #ifdef ZgatewayBT
     setupBT();
   #endif
@@ -249,6 +252,11 @@ void loop()
       if(resultRF)
       trc(F("RFtoMQTT OK"));
     #endif
+    #ifdef ZgatewayRF2
+      boolean resultRF2 = RF2toMQTT();
+      if(resultRF2)
+      trc(F("RF2toMQTT OK"));
+    #endif
     #ifdef ZgatewayIR
       boolean resultIR = IRtoMQTT();
       if(resultIR)