[V3 Admin] Rewrite of Squid-Plugins Admin cog (#825)

* Add/remove roles

* Announcement

* Edit role stuff

A bit of refactoring

* Selfrole stuff

* Add announce ignore capabilities

* announce configurations

Announcement fixes

* Serverlock initial commit

* Add some admin tests

better test

* Update for new config

* Add user hierarchy checks

* Fix tests

* Update from rebase

* Fix config getter

* Fix async getters/selfrole

redbot/cogs/admin/converters.py

@@ -0,0 +1,33 @@
+import discord
+from discord.ext import commands
+
+
+class MemberDefaultAuthor(commands.Converter):
+    async def convert(self, ctx: commands.Context, arg: str) -> discord.Member:
+        member_converter = commands.MemberConverter()
+        try:
+            member = await member_converter.convert(ctx, arg)
+        except commands.BadArgument:
+            if arg.strip() != "":
+                raise
+            else:
+                member = ctx.author
+        return member
+
+
+class SelfRole(commands.Converter):
+    async def convert(self, ctx: commands.Context, arg: str) -> discord.Role:
+        admin = ctx.command.instance
+        if admin is None:
+            raise commands.BadArgument("Admin is not loaded.")
+
+        conf = admin.conf
+        selfroles = await conf.guild(ctx.guild).selfroles()
+
+        role_converter = commands.RoleConverter()
+        role = await role_converter.convert(ctx, arg)
+
+        if role.id not in selfroles:
+            raise commands.BadArgument("The provided role is not a valid"
+                                       " selfrole.")
+        return role