tweak pixfader:

* update reserve so that round corners don't overlap
* draw complete 1px outline
* add API to hide/show the unity line
* don't show unity line at either end
* allow to shrink when the font-scaling changes
Barcontroller: no double expose when text chages
don't show 'unity-line' (default value) for barcontrollers
add a special bool option that prevents redrawing
dramatically speed up track-number show/hide toggle
get rid of a compiler warning