(core) Expanding widgets

Summary:
New icon to expand an active section and show it as a popup (just like raw data views).

"Show raw data" popup couldn't be reused (as it is basically a different page), so now
we have two kinds of popups that look the same.

1. Raw data popup - to show an alien section on a page (a section from a different view). This is used by "Show raw data" button, it is basically a different page that shows an arbitrary section.

2. Layout popup - a popup generated by Layout.ts that basically hides every other section and adds an overlay effect to itself.

Other changes
- Layout.js was migrated to typescript
- "Show raw data" menu item was converted to link

Test Plan: new tests

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3764

app/client/lib/koArray.d.ts

@@ -24,8 +24,10 @@ declare class KoArray<T> {
   public clampIndex(index: number): number|null;
   public makeLiveIndex(index?: number): ko.Observable<number> & {setLive(live: boolean): void};
   public setAutoDisposeValues(): this;
+  public arraySplice(start: number, deleteCount: number, items: T[]): T[];
 }
 
 declare function syncedKoArray(...args: any[]): any;
 
 export default function koArray<T>(initialValue?: T[]): KoArray<T>;
+export function isKoArray(obj: any): obj is KoArray<any>;