Upgraded RF24 to latest version which supports SoftSPI.
Added DigitalIO and UTFT libraries to support the new example.
Fix problem reported in RelayWithButtonActuator example.
- changed HEADER_SIZE constant from 8 to 7 to reflect message structure
- removed duplicate utility folder in UIPEthernet that prevented proper
compilation
- removed unnecessary includes in EthernetGateway that prevented proper
compilation