[Editor] - Add the ability to directly draw after selecting ink tool

- Right now, we must select the tool, then click to select a page and
  click to start drawing and it's a bit painful;
- so just create a new ink editor when we're hovering a page without one.

web/annotation_editor_layer_builder.css

@@ -98,6 +98,11 @@
   overflow: auto;
   width: 100%;
   height: 100%;
+  z-index: 1;
+}
+
+.annotationEditorLayer .background {
+  z-index: 0;
 }
 
 .annotationEditorLayer .inkEditor:focus {