(core): Add app-global setting storage.

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`.

bot/modules/sponsors/commands.py

@@ -1,7 +1,6 @@
 from cmdClient.checks import is_owner
 
 from .module import module
-from .config import settings
 
 
 @module.cmd(
@@ -18,10 +17,10 @@ async def cmd_sponsors(ctx, flags):
     if await is_owner.run(ctx) and any(flags.values()):
         if flags['edit']:
             # Run edit setting command
-            await settings.sponsor_message.command(ctx, 0)
+            await ctx.client.settings.sponsor_message.command(ctx, ctx.client.conf.bot['data_appid'])
         elif flags['prompt']:
             # Run prompt setting command
-            await settings.sponsor_prompt.command(ctx, 0)
+            await ctx.client.settings.sponsor_prompt.command(ctx, ctx.client.conf.bot['data_appid'])
     else:
         # Display message
-        await ctx.reply(**settings.sponsor_message.args(ctx))
+        await ctx.reply(**ctx.client.settings.sponsor_message.args(ctx))