(core) Comments

Summary:
First iteration for comments system for Grist.
- Comments are stored in a generic metatable `_grist_Cells`
- Each comment is connected to a particular cell (hence the generic name of the table)
- Access level works naturally for records stored in this table
-- User can add/read comments for cells he can see
-- User can't update/remove comments that he doesn't own, but he can delete them by removing cells (rows/columns)
-- Anonymous users can't see comments at all.
- Each comment can have replies (but replies can't have more replies)

Comments are hidden by default, they can be enabled by COMMENTS=true env variable.
Some things for follow-up
- Avatars, currently the user's profile image is not shown or retrieved from the server
- Virtual rendering for comments list in creator panel. Currently, there is a limit of 200 comments.

Test Plan: New and existing tests

Reviewers: georgegevoian, paulfitz

Reviewed By: georgegevoian

Subscribers: paulfitz

Differential Revision: https://phab.getgrist.com/D3509

app/common/schema.ts

@@ -4,7 +4,7 @@ import { GristObjCode } from "app/plugin/GristData";
 
 // tslint:disable:object-literal-key-quotes
 
-export const SCHEMA_VERSION = 32;
+export const SCHEMA_VERSION = 33;
 
 export const schema = {
 
@@ -196,6 +196,17 @@ export const schema = {
     filter              : "Text",
   },
 
+  "_grist_Cells": {
+    tableRef            : "Ref:_grist_Tables",
+    colRef              : "Ref:_grist_Tables_column",
+    rowId               : "Int",
+    root                : "Bool",
+    parentId            : "Ref:_grist_Cells",
+    type                : "Int",
+    content             : "Text",
+    userRef             : "Text",
+  },
+
 };
 
 export interface SchemaTypes {
@@ -388,4 +399,15 @@ export interface SchemaTypes {
     filter: string;
   };
 
+  "_grist_Cells": {
+    tableRef: number;
+    colRef: number;
+    rowId: number;
+    root: boolean;
+    parentId: number;
+    type: number;
+    content: string;
+    userRef: string;
+  };
+
 }