Concept : cooperative mt scheduler with events V2

- Non preemtive mt-scheduler (context switch during irq not allowed for this implementation)
- In this implementation the cmt thread is derived from contiki process, thus a thread uses the contiki process scheduler instead of an own scheduler.
- As a cmt instance is also a process instance, process post/post_sync can be used directly by processes and cmt_threads to post events to each other.
- This example also shows the close logical relationship between protothreads and usual cooperative threads. Think twice if you really need context switching or not!
-  For this special example it would be an advantage if process functions would use a void pointer for process passing, to avoid explicit casting on application level.
- It would be an advantage to be able to define thread specific stack sizes to avoid unnecessary RAM usage. Maybe by using cpu min stack size and multiplier? ... to be discussed