(core) Adding colors to toast notification

Summary:
Styling toast notification. Adding colors and icons.
In Grist, changed the default style for errors (will be shown in red), and a style for
Linked copied to clipboard (will be shown in Green).
All other colors are not used currently, left for another diff.

Test Plan: manual

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3053

app/client/components/Drafts.ts

@@ -270,7 +270,7 @@ class NotificationAdapter extends Disposable implements Notification {
   }
   public showUndoDiscard() {
     const notifier = this._doc.app.topAppModel.notifier;
-    const notification = notifier.createUserError("Undo discard", {
+    const notification = notifier.createUserMessage("Undo discard", {
       message: () =>
         discardNotification(
           dom.on("click", () => {