Scheduler

A big pull request for the scheduler !

This should fix the issues #15, #30, #39 and #40.

The Scheduler test for AVR has been updated (new makefile, check several tasks).
The Scheduler test for SASIAE has also been updated (check several tasks).

To sum up modifications : 
- The scheduler is now configurable with a "Config" structure passed as a template parameter.
- The main part of the code has been moved to common branch.
- A lot of debug about prescalers.