update slider rendering & set style for faders

* render background -- outside of rounded corners
* visually align unity-location with fader at 0.
* sharp lines (no more AA blur) x/y offset, radius
fix fader default-value line position
update processor control toggle button style
processor-box wiring - re-use colors from ingen/patchage
more processor-routing tweaks: compact view

* hide 'input' ports if mapping matches
 -> display half circles
* show ports for top-most processor (allos insertion point)
* reduce line-size to 1.0 and routing-box height to 7 (cairo .5 px align)
processor-box: remove cruft