[ivette] ranked extension points

ivette/src/renderer/Extensions.tsx

@@ -133,9 +133,12 @@ function byPanel(p: ElementProps, q: ElementProps) {
 
 export class ElementRack {
 
+  private rank = 1;
   private readonly items = new Map<string, ElementProps>();
 
   register(elt: ElementProps) {
+    if (elt.rank === undefined) elt.rank = this.rank;
+    this.rank++;
     this.items.set(elt.id, elt);
     UPDATED.emit();
   }