Bar hover tooltip

The goal was to have them work for HorizontalBar plots as well, but Category axes don't play nice with range changes.

To use tooltips, project the desired text onto the "tooltip-text" property. Extra space will be allocated above the bars for the tooltip.

Mousemove Interaction has been changed to a Mouse Interaction with mouseover, mousemove, and mouseout callbacks.

The architecture still needs to be improved. The plan is to keep the current implementation on a side branch, and create releases pointed at that for people who need the tooltips sooner.