Improve autoScroll, styleCursor and other options

- autoscroll and styleCursor can be set globally and per Interactable.
- Added 'container' property for autoScroll option which allows you to
set the element that is scrolled when the mouse is `action`ed to it's
edges.
- The cursor is not set for each element but instead only for the
documentElement. The style is also now '!important'.
README: be honest about modifying cursor style