[Frontend] Significant mods to main layout strategy

open #90
IN-PROGRESS
To support desired edge-to-edge styling of Inspector pane;
Removed superflous .scss file;
Enhancements to splitter .scss to allow flush edging and
edge shadows;

platform/commonUI/general/res/sass/_inspector.scss

@@ -27,6 +27,8 @@
 }
 
 .l-inspect {
+    background: pullForward($colorBodyBg, 3%);
+    @extend .abs;
     color: $colorInspectorFg;
     .pane-header {
         color: pushBack($colorInspectorFg, 20%);