(core) Adding font options to the style picker

Summary:
Redesigning color picker:
- Single color palette (no light/dark switch)
- Ability to remove color (new empty button)

New font options in the color picker.
Font options are available on:
- Default cell style
- Conditional rules styles
- Choice/ChoiceList editor and token field
- Filters for Choice/ChoiceList columns

Design document:
https://www.figma.com/file/bRTsb47VIOVBfJPj0qF3C9/Grist-Updates?node-id=415%3A8135

Test Plan: new and updated tests

Reviewers: georgegevoian, alexmojaki

Reviewed By: georgegevoian, alexmojaki

Subscribers: alexmojaki

Differential Revision: https://phab.getgrist.com/D3335

app/client/widgets/AbstractWidget.js

@@ -14,6 +14,7 @@ function AbstractWidget(field, opts = {}) {
   const {defaultTextColor = '#000000'} = opts;
   this.defaultTextColor = defaultTextColor;
   this.valueFormatter = this.field.visibleColFormatter;
+  this.defaultTextColor = opts.defaultTextColor || '#000000';
 }
 dispose.makeDisposable(AbstractWidget);