many changes related to #1192:

- use CSS contain wherever possible to reduce subtrees of forced reflows
- reduced dependency between note and note_contents updates which will reduce number of updates to components
- optimization of "many rows" querying

src/public/app/widgets/basic_widget.js

@@ -25,6 +25,11 @@ class BasicWidget extends Component {
         return this;
     }
 
+    contentSized() {
+        this.css('contain', 'layout paint');
+        return this;
+    }
+
     collapsible() {
         this.css('min-height', '0');
         return this;