(core) Fixing couple of bugs in collapsed section layout

Summary:
The previous implementation for collapsing sections involved disposing of a view instance (Grid or Chart component). This caused numerous bugs with
linking sections as the implementation is located in the BaseView.js. Now the view instance is kept and attached to a dom in a hidden div, so it can respond
and function as a normal rendered section. It is also passed from between collapsed and main layout, when sections are dragged or moved using section's
menu commands (`collapse` and `add to main page`)

It also implies that the ViewLayout must still be rendered when a section is maximized (as it is responsible for the view instance), so the dom, and
some logic for rendering it, had to be changed.

Test Plan: New and updated

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3826

app/client/lib/Signal.ts

@@ -109,6 +109,7 @@ export class Signal<T = any> implements IDisposable, IDisposableOwner {
    */
   public pipe(signal: Signal<T>) {
     this.autoDispose(this.listen(value => signal.emit(value)));
+    return this;
   }
 
   /**