(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/ui2018/cssVars.ts

@@ -168,7 +168,7 @@ export const mediaXSmall = `(max-width: ${smallScreenWidth - 0.02}px)`;
 
 export const mediaDeviceNotSmall = `(min-device-width: ${mediumScreenWidth}px)`;
 
-function isNarrowScreen() {
+export function isNarrowScreen() {
   return window.innerWidth < mediumScreenWidth;
 }