feature (sponsors): Add sponsor command.

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`.

bot/modules/__init__.py

@@ -13,3 +13,4 @@ from .renting import *
 from .moderation import *
 from .accountability import *
 from .plugins import *
+from .sponsors import *