CPU consuming work is being done in `scene2d.draw`

[monfera]

The issue is present if there's a large number of items to show and hovermode is not false. The requestAnimationFrame loop seems to repeat tasks, some of which would need to be done only if something pertinent changed, for example, the user moved the mouse and this necessitated the display of a different hover tooltip (for another scatterpoint).

[monfera]

#731 purports to fix the high CPU utilization (in the case of 1m points: from 100% to 5%). it seems a sufficient initial solution. If time permits, or fast incremental loading mandates, we can revisit the rAF loop for further reduction or elimination.

[etpinard]

Closed (for now) by #731