* Fix behavior while the button is invisible
e.g. pointer cursor, couldn't open contextmenu
* Avoid rendering the button to remove blank space if no more items are available or no items are rendered
Resolved:
* Lot of redundant renders while mouse moving
* Scroll jumping when timeline loaded
* Scroll position isn't kept when statuses below the scrollTop was deleted then new status arrived
Unresolved:
* Scroll position isn't kept when statuses over the scrollTop was deleted then new status arrived
-> It needs to know which statuses are over the scrollTop
* New status indicator should be active when new statuses arrived while mouse moved recently
-> It needs a) update indicator in ScrollableList, or b) set scrollTop status while mouse moving
