Introduce callbacks to hide and show container.

[widoz]

Instead of using the "on" callbacks that for hide and show behavior, allowing a callback will prevent the original functions to be called.

So for example, if I want to use slideUp/slideDown the animate effect will not be performed because the show/hide will be performed before the animated functions.

[widoz]

If a valid feature I think will be possible to create new wrapper functions for show and hide.

Also, I used the "container" object as this for the function, may be pass as parameter is better?