... (i.e. out of plot_api.js),
    and move Plots.addLinks out of drawData into its own
    step in Plotly.plot.

- this represents the minimal sequence for '(x|y)axis.range'
  relayout calls which are pretty common (e.g. on zoom/pan
  mouseup).
- by bypassing drawFramework, lsInner and initInteraction,
  this can save ~1000ms on 50x50 subplot grids.

- split minimal updateFx part out of initInteractions
- set maindrag cursor class (which depends only on layout.dragmode)
  on <g .draglayer> instead of inner <rect> to update it for
  all subplots in < 1ms (that's a > 600ms improvement on 50x50 grids)
- use gd._fullLayout instead of scoped fullLayout in initInteractions
  and makeDragBox to ensure correct reference after doModeBar()

- allow fullLayout._has(/*trace type*/) to work
- use registry category hash object (instead of categories.indexOf)
  to find categories in fullLayout._modules

- replace indexOf with hash objects lookups
- add 'svg' and 'draggedPts' trace module categories
- speed up updateSubplots (called on pan and scroll) by
  splitting it into splom, scattergl, svg and draggedPts blocks,
  (draggedPts is very slow, svg can be slow at 50x50)
- ... some scope variable clean up

(to get tests to pass)