feat(follow): add feed links, following page and tile (#52, #51)

Feed links go to the game and to the profile view of that game.
Add /following page, nav item and an opt-in Following tile.
Games not in your library show a catalog view with an add button.

src/components/AppHeader.test.jsx

@@ -49,6 +49,12 @@ describe('AppHeader', () => {
         expect(screen.queryByTitle('NAV.COMMUNITY')).toBeNull();
     });
 
+    it('links to the following page when logged in', () => {
+        loggedInAs({role: 'USER', activeRole: 'USER'});
+
+        expect(screen.getByTitle('NAV.FOLLOWING').getAttribute('href')).toBe('/following');
+    });
+
     it('links to the community stats when logged in', () => {
         loggedInAs({role: 'USER', activeRole: 'USER'});