Adding of Effect operator

==, <, >, <=, >= operators have been added
Scheduler: Data structure has been added

Schduler data structure has been changed from boost::heap to std::vector.
Scheduler: update and exists function added

Element can now be updated by using 'update' function. Scheduler can contain
only one time an element (use 'exists' function to check if an element is
present in the scheduler).
Ball model: update ball effects

Collision effects are now updated between balls. Another example has been added.