implemented match method in Stackable.
implemented before filters.
add return and argument types.
remove ApplyFilterTrait (before filter is in Stackable) and other untested classes.
renamed Stackable to Stack class.
match and before shall return $this.
renamed StackableInterface to StackInterface (as class name changed...)
created Service namespace to store classes for services.
App::start method to set up config as locator.