Add new scene controller with touch display example.

Upgraded RF24 to latest version which supports SoftSPI. 
Added DigitalIO and UTFT libraries to support the new example.
Fix problem reported in RelayWithButtonActuator example.

libraries/DigitalIO/examples/DigitalPinBlink/DigitalPinBlink.ino

@@ -0,0 +1,12 @@
+#include <DigitalIO.h>
+// Create object for pin 13 in output mode and demo toggle().
+DigitalPin<13> pin13(OUTPUT);
+
+void setup() {}
+
+void loop() {
+  // toggle is a two byte instruction that executes
+  // in two cycles or 125 ns on a 16 MHz CPU
+  pin13.toggle();
+  delay(250);
+}