[Admin] Code prettification and bugfixing (#3250)

* Facelift for Admin

* Remove unnecessary converter, reorder existing steps

* Delete admin.py

* Delete __init__.py

* Delete test_admin.py

* Remove one extra unneeded check

* Create 3250.bugfix.1.rst

* Create 3250.bugfix.2.rst

* Create 3250.bugfix.3.rst

* Create 3250.bugfix.4.rst

* Create 3250.misc.1.rst

* Create 3250.misc.2.rst

* Create 3250.misc.3.rst

* Create 3250.breaking.1.rst

* Create 3250.breaking.2.rst

* ...

* I hate black...

tests/cogs/admin/test_admin.py

@@ -1,44 +0,0 @@
-from unittest.mock import MagicMock
-
-import pytest
-
-from redbot.pytest.admin import *
-
-
-@pytest.mark.asyncio
-async def test_serverlock_check(admin, coroutine):
-    await admin.conf.serverlocked.set(True)
-    guild = MagicMock()
-    guild.leave = coroutine
-
-    # noinspection PyProtectedMember
-    ret = await admin._serverlock_check(guild)
-
-    assert ret is True
-
-
-def test_announcer_initial_state(announcer):
-    assert announcer.active is None
-
-
-def test_announcer_start(announcer):
-    announcer.announcer = object
-    announcer.start()
-
-    assert announcer.ctx.bot.loop.create_task.called
-    assert announcer.active is True
-
-
-@pytest.mark.asyncio
-async def test_announcer_ignore(announcer, empty_guild, empty_channel):
-    await announcer.config.guild(empty_guild).announce_channel.set(empty_channel.id)
-
-    guild = MagicMock()
-    guild.id = empty_guild.id
-
-    guild.get_channel.return_value = empty_channel
-
-    ret = await announcer._get_announce_channel(guild)
-
-    assert guild.get_channel.called
-    assert ret == empty_channel