DoNotPaint scriptSlider option

[ustk]

@Christoph-Hart Is it acceptable to add an option to make sliders transparent.
A new entry in the filmstripImage selection would be cool. I often use ghost sliders on top of panels like you did for Hexeract so each time I create a new project or just to test ideas I have to import an empty filmstrip... A transparent option would be nice here and can be easily set via JSON when adding new sliders

[d.healey]

@ustk What's wrong with the transaparent .png? Works for buttons too.

[ustk]

@d-healey Well there's nothing really wrong, it is just that you need to import the .png each time you test a new idea/project (which I do a lot) or for providing snippets.
A "make transparent" option is just an easier shortcut