(core) Enable auto triggering of Welcome Tour, and various improvements.

Summary:
- Add showGristTour preference, and trigger tour automatically.
- Tour is only triggered for new and anonymous users on a personal org, with
  edit permission.

- Automatically open the right panel at tour start.
- Don't show tours on mobile, since that's not ready (popups are cut off
  and can't be dismissed)
- Cancel previous tour if a new one is somehow started.
- Remove #repeat- trigger hash tags from the URL when the tour starts.
- Ensure Help Center popup is positioned even when left panel is collapsed.
- Polish up the content of the last two cards in the tour.

Test Plan: Added test case for triggering and opening right panel.

Reviewers: alexmojaki, paulfitz

Reviewed By: alexmojaki

Differential Revision: https://phab.getgrist.com/D2955

app/client/ui/RightPanel.ts

@@ -183,7 +183,7 @@ export class RightPanel extends Disposable {
 
   private _buildFieldContent(owner: MultiHolder) {
     const fieldBuilder = owner.autoDispose(ko.computed(() => {
-      const vsi = this._gristDoc.viewModel.activeSection().viewInstance();
+      const vsi = this._gristDoc.viewModel.activeSection?.().viewInstance();
       return vsi && vsi.activeFieldBuilder();
     }));
 
@@ -197,7 +197,7 @@ export class RightPanel extends Disposable {
 
     // build cursor position observable
     const cursor = owner.autoDispose(ko.computed(() => {
-      const vsi = this._gristDoc.viewModel.activeSection().viewInstance();
+      const vsi = this._gristDoc.viewModel.activeSection?.().viewInstance();
       return vsi?.cursor.currentPosition() ?? {};
     }));