(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

static/ui-icons/UI/Empty.svg

@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg
+   xmlns:svg="http://www.w3.org/2000/svg"
+   xmlns="http://www.w3.org/2000/svg"
+   width="20"
+   height="20"
+   viewBox="0 0 5.2916665 5.2916668">
+  <defs
+     id="defs2" />
+  <g
+     id="layer1"
+     transform="translate(0,-291.70832)">
+    <path
+       style="fill:none;stroke:#000000;stroke-width:0.5291667;stroke-linecap:butt;stroke-linejoin:miter;stroke-miterlimit:4;stroke-dasharray:none;stroke-opacity:1;paint-order:normal"
+       d="m 0.03262263,291.72225 5.23003227,5.2769" />
+  </g>
+</svg>