[communication] [superbus] [Xbee_API] Integrates Xbee with api mode 2 in superBus :  
* Clears old superBus_Xbee files from Xbee resources and renames them in UARTxxx et enable superbus over UART.
* Creates Xbee4sb.cpp/.h, defining functions to use Xbee in superBus.
* Modifies the README_SUPERBUS accordingly.
* Adds UART support in superBus.c:.h and in networkConfig.h.
* Modifies project properties accordingly.