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

User_config.h

@@ -95,7 +95,7 @@ const byte subnet[] = { 255, 255, 255, 0 }; //ip adress
 #else // for arduino + W5100
   #define ZgatewayRF
   #include "config_RF.h"
-  #define ZgatewayRF2
+  //#define ZgatewayRF2 // too big for UNO
   #ifdef RFM69_Wiring
     //#define ZgatewayRFM69 not tested
     //#include "config_RFM69.h"