Update discord.py version to 1.2.3

I have updated the discord.py version to 1.2.3. This includes changes
throughout the entire code base, including:

- All cogs now inherit from `discord.ext.commands.Cog`;

- All of our ABCs now have `bot.utils.CogABCMeta` as a metaclass;

- All event handlers in cogs are now decorated with `Cog.listener()`;

- Some method names have changes, including:

  - get_message => fetch_message
  - get_webhook_info => fetch_webhook

- A few occurences of `get_channel` have been replaced by the new
  coroutine `fetch_channel`;

- I've had to patch a few lines of code to account for small
  differences between the versions, like `on_member_update` attribute
  names in ModLog and the fact the way we used `Context.invoke` a couple
  of times has stopped working.

In addition, I've added a patch for a bug in discord.py (with the help
of @Scragly). This discord.py version has a bug which causes the edited
timestamp not to be processed for edited messages. It's already fixed
on GitHub, but a bug fix release has not been released to PyPI. In the
meantime, I've added a patch in `bot.patches.message_edited_at` and
included conditional loading in `__main__`.

Finally, I noticed a small bug in `bot.cogs.filtering` that I fixed; I
replaces `return` with `continue` to make sure filtering for edited
messages doesn't stop after the `rich_embed_filter`.

1 files changed, 4 insertions, 3 deletions

diff --git a/bot/cogs/moderation.py b/bot/cogs/moderation.py
index 532a44f4d..fcbadd235 100644
--- a/bot/cogs/moderation.py
+++ b/bot/cogs/moderation.py
@@ -8,7 +8,7 @@ from discord import (
     Colour, Embed, Forbidden, Guild, HTTPException, Member, NotFound, Object, User
 )
 from discord.ext.commands import (
-    BadArgument, BadUnionArgument, Bot, Context, command, group
+    BadArgument, BadUnionArgument, Bot, Cog, Context, command, group
 )
 
 from bot import constants
@@ -46,7 +46,7 @@ def proxy_user(user_id: str) -> Object:
 UserTypes = Union[Member, User, proxy_user]
 
 
-class Moderation(Scheduler):
+class Moderation(Scheduler, Cog):
     """
     Server moderation tools.
     """
@@ -60,6 +60,7 @@ class Moderation(Scheduler):
     def mod_log(self) -> ModLog:
         return self.bot.get_cog("ModLog")
 
+    @Cog.listener()
     async def on_ready(self):
         # Schedule expiration for previous infractions
         infractions = await self.bot.api_client.get(
@@ -1348,7 +1349,7 @@ class Moderation(Scheduler):
         """
 
         # sometimes `user` is a `discord.Object`, so let's make it a proper user.
-        user = await self.bot.get_user_info(user.id)
+        user = await self.bot.fetch_user(user.id)
 
         try:
             await user.send(embed=embed)