Liquify v1.2

I've seen several different tools on here seeking to replicate the 'liquify' brush effect. In essence, they're all ways of editing an STmap with a RotoPaint node, and using that to drive an IDistort.

This version is pretty similar, but manages to do it with a bit more of a streamlined workflow by placing the relevant RotoPaint knobs onto the main tab. This lets you work with it similarly to a normal node, without having to pipe in a painted-on STmap or open up a Group to edit a RotoPaint separately. Includes controls to scale, smooth, and smear the warp, as well as just painting it.

Whilst I think this gizmo is a bit nicer than other ways I've seen 'liquify' done before, it does have some issues. It's better, not perfect.

Known issues (with some workarounds):

• the rotopaint knobs, when shown, override the 'D' hotkey to disable a node.
  • I placed the knobs inside a 'Paint Controls' Group Knob for when you aren't painting. This makes it behave more normally
• When a brush stroke is selected, a transform widget is shown in the middle of the viewer
  • You can move the widget without it affecting any of the brushstrokes
  • Collapsing the 'Paint Controls' Group hides this viewer overlay
  • Deselecting the selected brushstroke removes the overlay
• Having several liquifies open in Properties simultaneously can cause unpredictable paint behaviour
  • Same as for Rotos and RotoPaints: keep one open at a time