(guild admin): Add greeting messages.

New `SettingType` `Message` for general message settings.
New setting `greeting_message`.
New setting `greeting_channel`.
New setting `starting_funds`.
New setting `returning_message`.
Add a greeting message hook.
Add initial funds on lion creation.
Data migration v3 -> v4.

bot/modules/guild_admin/__init__.py

@@ -2,3 +2,4 @@ from .module import module
 
 from . import guild_config
 from . import statreset
+from . import utils