Expire anonymous decomps

[maxveldink]

If someone creates an anonymous decomp, we should expire these after a configurable amount of time (let's default to 48 hours).

AC:

• Any decomp not owned by a user is automatically deleted after 48 hours
• Expiration time is easily configurable
• If someone has a decomp id in their session that's been deleted, don't navigate to it and delete it from the session