New `AppConfig` key-value table for arbitrary app config.
New `KeyValueData` setting data mixin.
New `AppSettings` settings group.
Attached `AppSettings` as `client.settings`.
Migrated sponsor settings to `AppSettings`.
Add new sponsor prompts.
Add new sponsor command.
Add `sponsor_text` table.
Add sponsor global config settings.
Update `Setting.command` to use new `widget`.
Add custom `cmd_str` support to `Message` `SettingType`.
