Update raw example
Update raw example

By setting some more parameters (frequency, txpower), RX and TX now work
properly. Whenever a packet is received, reception is now restarted.

It now also updates leds to indicate reception status. The led is red (on
Pinoccio, or off for normal Arduino boards) when no packet was received
in 2500ms, green (or off) when there was. Whenever a packet is received, the LED
very briefly blinks to indicate this.

Packets are sent about once every second. When a packet is received, the
next TX is rescheduled to prevent TX collisions (in a very basic way).

mcci-catena/arduino-lmic,mcci-catena/arduino-lmic,mcci-catena/arduino-lmic