(core) Forms improvements

Summary:
Forms improvements and following new design
- New headers
- New UI
- New right panel options

Test Plan: Tests updated

Reviewers: georgegevoian, dsagal

Reviewed By: georgegevoian

Subscribers: dsagal, paulfitz

Differential Revision: https://phab.getgrist.com/D4158

app/plugin/gutil.ts

@@ -7,3 +7,5 @@ import times = require('lodash/times');
 export function arrayRepeat<T>(count: number, value: T): T[] {
   return times(count, constant(value));
 }
+
+export type MaybePromise<T> = T | Promise<T>;