Use scroll container 's properties

[HaroldLever]

https://github.com/SpyrexDE/SmoothScroll/assets/80692930/7930d847-cbfa-4e8e-877a-6af7a075a0ca

ScrollContainer on left, SmoothScrollContainer on right.

scroll_horizontal and scroll_vertical now should work

• I noticed that several users (#48 #56) are confused with these two properties not working, I made a minor change to make it work just like scroll container.

scroll_deadzone now should work

Replaces SmoothScrollContainer.follow_focus_ by ScrollContainer.follow_focus

• Since SmoothScrollContainer.follow_focus_ is removed, this is not a compatible change.
• The default value of SmoothScrollContainer.follow_focus_ is true, while ScrollContainer.follow_focus is false. Should beware.
• BTW, why don't use ScrollContainer.follow_focus at that time.

Overrides ScrollContainer.ensure_control_visible, now it should work.

InputEventMouseButton.factor is taken into calculation.

[SpyrexDE]

Those are good changes. I didn't know that you could override _get() to achieve this but it seems to work fine. Thanks :)