Add a mojit: An almost empty file at /

http://localhost:8666/ has HTML page now (instead of 404).
Add a very simple session addon.

This addon does have its drawbacks:
- Limit of 1000 sessions.
- In-memory store.
- Session validation only through cookie, and cookie remains same
throughout the session.

Despite these shortcomings, it works as a proof-of-concept, which is
just enough for me at this stage.