[Frontend] Manual re-do of collapse/expand panes

open #90
Major work on new .mini-tab elements, used
as controls to expand/collapse panes;
Cleaned up splitter hover behavior;
Changed mixin controlGrippy to not be tied
to :before;

platform/commonUI/general/res/sass/controls/_controls.scss

@@ -306,8 +306,6 @@ label.checkbox.custom {
 		left: 0;
 	}
 	.knob {
-		//@include btnSubtle();
-		//@include controlGrippy(rgba(black, 0.3), vertical, 1px, solid);
 		@include trans-prop-nice-fade(.25s);
 		background-color: $sliderColorKnob;
 		&:hover {