(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/models/Styles.ts

@@ -1,18 +1,34 @@
 export interface Style {
   textColor?: string;
   fillColor?: string;
+  fontBold?: boolean;
+  fontUnderline?: boolean;
+  fontItalic?: boolean;
+  fontStrikethrough?: boolean;
 }
 
 export class CombinedStyle implements Style {
   public readonly textColor?: string;
   public readonly fillColor?: string;
-  constructor(rules: Style[], flags: any[]) {
+  public readonly fontBold?: boolean;
+  public readonly fontUnderline?: boolean;
+  public readonly fontItalic?: boolean;
+  public readonly fontStrikethrough?: boolean;
+  constructor(rules: (Style|undefined|null)[], flags: any[]) {
     for (let i = 0; i < rules.length; i++) {
       if (flags[i]) {
-        const textColor = rules[i].textColor;
-        const fillColor = rules[i].fillColor;
+        const textColor = rules[i]?.textColor;
+        const fillColor = rules[i]?.fillColor;
+        const fontBold = rules[i]?.fontBold;
+        const fontUnderline = rules[i]?.fontUnderline;
+        const fontItalic = rules[i]?.fontItalic;
+        const fontStrikethrough = rules[i]?.fontStrikethrough;
         this.textColor = textColor || this.textColor;
         this.fillColor = fillColor || this.fillColor;
+        this.fontBold = fontBold || this.fontBold;
+        this.fontUnderline = fontUnderline || this.fontUnderline;
+        this.fontItalic = fontItalic || this.fontItalic;
+        this.fontStrikethrough = fontStrikethrough || this.fontStrikethrough;
       }
     }
   }