Fixed rssi scanner application and moved into single example

This fix issue https://github.com/contiki-os/contiki/issues/869 related to a broken RSSI scanner example after replacing cc2420-specific macros.  Also merges the Z1 and Sky example examples into single cc2420-based example, allowing other platforms to reuse the ViewRSSI java application by implementing its own rssi scanner.

Tested on Z1, it compiles for sky.