Implement editions in the backend.

[jnms-me]

Add a database table for editions:

• id
• name (string, [0-9a-z]+)
• running (bool)
• public (bool)
• rules (markdown)
• contact info (markdown)
• sponsors (markdown)

Have every question be linked to an edition.
Have every team be linked to one or multiple editions.

Prefix all paths with the edition name, except for:

• /, which redirects to the newest edition.
• /login.