(core) Show a welcome card when a user opens an example for the first time.

Summary:
- The card includes an image, a brief description, and a link to the tutorial.
- The left panel includes a link to the tutorial, and a button to reopen card.
- Card is collapsed and expanded with a little animation.
- Add a seenExamples pref for whether an example has been seen.
- Store the pref in localStorage for anon user.

Separately, added clearing of prefs of test users between tests, to avoid tests
affecting unrelated tests.

Test Plan: Added a browser test.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2602

app/client/ui/transitions.ts

@@ -57,22 +57,31 @@ export function transition<T>(obs: BindableValue<T>, trans: ITransitionLogic<T>)
       });
 
       // Call prepare() with transitions turned off.
+      prepareForTransition(elem, () => prepare(elem, val));
+    }
+    run(elem, val);
+  });
+}
+
+/**
+ * Call prepare() with transitions turned off. This allows preparing an element before another
+ * change to properties actually gets animated using the element's transition settings.
+ */
+export function prepareForTransition(elem: HTMLElement, prepare: () => void) {
   const prior = elem.style.transitionProperty;
   elem.style.transitionProperty = 'none';
-      prepare(elem, val);
+  prepare();
 
   // Recompute styles while transitions are off. See https://stackoverflow.com/a/16575811/328565
   // for explanation and https://stackoverflow.com/a/31862081/328565 for the recommendation used
   // here to trigger a style computation without a reflow.
   window.getComputedStyle(elem).opacity;   // tslint:disable-line:no-unused-expression
 
-      // Restore transitions before run().
+  // Restore transitions.
   elem.style.transitionProperty = prior;
-    }
-    run(elem, val);
-  });
 }
 
+
 /**
  * Helper for waiting for an active transition to end. Beyond listening to 'transitionend', it
  * does a few things:
@@ -86,7 +95,7 @@ export function transition<T>(obs: BindableValue<T>, trans: ITransitionLogic<T>)
  * When the transition ends, TransitionWatcher disposes itself. Its onDispose() method allows
  * registering callbacks.
  */
-class TransitionWatcher extends Disposable {
+export class TransitionWatcher extends Disposable {
   private _propertyName: string;
   private _durationMs: number;
   private _timer: ReturnType<typeof setTimeout>;

app/common/Prefs.ts

@@ -18,6 +18,11 @@ export type UserPrefs = Prefs;
 export interface UserOrgPrefs extends Prefs {
   docMenuSort?: SortPref;
   docMenuView?: ViewPref;
+
+  // List of example docs that the user has seen and dismissed the welcome card for.
+  // The numbers are the `id` from IExampleInfo in app/client/ui/ExampleInfo.
+  // By living in UserOrgPrefs, this applies only to the examples-containing org.
+  seenExamples?: number[];
 }
 
 export type OrgPrefs = Prefs;

app/gen-server/lib/HomeDBManager.ts

@@ -336,6 +336,21 @@ export class HomeDBManager extends EventEmitter {
     throw new Error(`Cannot testGetId(${name})`);
   }
 
+  /**
+   * Clear all user preferences associated with the given email addresses.
+   * For use in tests.
+   */
+  public async testClearUserPrefs(emails: string[]) {
+    return await this._connection.transaction(async manager => {
+      for (const email of emails) {
+        const user = await this.getUserByLogin(email, undefined, manager);
+        if (user) {
+          await manager.delete(Pref, {userId: user.id});
+        }
+      }
+    });
+  }
+
   public getUserByKey(apiKey: string): Promise<User|undefined> {
     return User.findOne({apiKey});
   }