Visual difference in `rslider`

[brylie]

When exporting a Rack module with rslider widget, the Rack module slider has several differences:

• thicker green line - may cause layout issues
• shade of green is different - not crucial, but could be consistent
• internal knob has "notch" - might be a good addition for the original Cabbage widget

Of the three differences noted above, only the line thickness seems substantive, as it can cause differences in the module layout and necessary width.

However, it would seem important for there to be visual consistency between the original and export.

[rorywalsh]

I'll take a look at this.