Move directory test_ZB500 in example/cc2530dk/zb500/
Rename files and directory to follow the syntax of contiki

Implement the bumpers management of zb500 in files:
- platform/cc2530dk/dev/button-sensor.c
- platform/cc2530dk/dev/button-sensor.h
- platform/cc2530dk/dev/smartrf-sensors.c

The example to use bumpers is:
- examples/cc2530dk/zb500/bumper/bumper.c