Auto whitelist preview, database support

With this release comes the database storage type support for automatic whitelisting.

Here we introduce migrations module and the very first migration will change your whitelist tables schema, resulting in two column name changes:

• whitelist.uniqueId -> whitelist.unique_id;
• whitelist.expiresAt -> whitelist.expires_at.

If you use some backend service to update the database, you will need to update your data access layer.

Other than that, this release introduces two new tables:

• migrations that stores finished migrations;
• auto_whitelist that stores the number players were automatically whitelisted.

Full Changelog: v0.9.5...v1.0.0a2