Make Arduino timer stuff work on Contiki

New discovery: Contiki also uses timer 0. With almost the same interface
as Arduino. So we now completely get rid of wiring.c (only the main
file, the other wiring_xxx stay) and implement Arduino timer, delay, etc
in terms of the corresponding Contiki routines. Verified that now delay
works as expected. The LED in examples/osd/arduino-sketch blinks!

Before this, the arduino_init routine in wiring.c destroyed the timer-0
initialization of contiki, making both, contiki timer implementation
*and* contiki timer implementation fail if the arduino_init routine was
called. Now both work.

Squashed with following bug-fix commit.

apps/arduino/arduino-process.c

@@ -50,6 +50,8 @@
  */
 
 #include "arduino-process.h"
+#include "hw_timer.h"
+#include "hw-arduino.h"
 
 PROCESS(arduino_sketch, "Arduino Sketch Wrapper");
 
@@ -57,7 +59,7 @@ PROCESS_THREAD(arduino_sketch, ev, data)
 {
   PROCESS_BEGIN();
 
-  arduino_init ();
+  arduino_pwm_timer_init ();
   setup ();
   while (1) {
     loop ();