uplot-vplugins

* Changed default draw-stage for annotation to "afterAll".

* Added "afterClear" and "afterAll" draw-stage options.

* Added "drawStage" field to annotation entries, allowing for them to be drawn prior to the series being drawn. (rather than using the drawType = "destination-over" approach, which can cause opacity-modifying effects)

* MS user can customize which mouse-buttons can start a pan, in the PanAndZoom plugin.

* Changed the three plugins to use classes, rather than plain functions.