Scheduling works without aperiodics.

(I know I'm commiting too much. No time to verify each one of the changes.
I didn't commit before because I was never sure if everything was "stable" or not)

1.  Remade the table parser
2.  Defined the needed data structures
3.  Timer callback now updates the current slot and current interval
4.  Writing 1 in the "/proc/litmus/plugins/SLOT-SHIFTING/start file starts the
    scheduling
5.  The "_init" functions, which initialize the "global" data, are now also
    initializing their new variables (look at the second item of this list)
6.  Offline guaranteed tasks are now initialized in the intervals when they
    become real time. The aperiodic tasks
7.  admit_task, task_new, task_exit, task_wake_up, task_lock and schedule
    functions were inserted.

+ Important: writing more than once in the table files leaks memory
    (look at "proc_write_table()" for more info)
+ Acceptance test (and related functions) are NOT working!