feat: better loading behavior overall

[RaymondWHZ]

Checklist:

• [x] Use server-side render for the home page, fixes #72;
• [x] Add spinner loading animation for the dashboard page and event detail page when loading user session and redirect;
• [x] Add skeleton loading animation for the event list and the whole event detail page, fixes #76;
• [x] Add a simple empty placeholder for the event list (enough for now), fixes #51;
• [x] Correctly handle 404 not found for event detail page (but did not add customized 404 page yet);
• [x] Minor updates on page layouts.

Some of the above need to be tested in production build, so please run build and then start to test them correctly!