[Audio] Connect to lavalink in the background (#2460)

Also:
- restart and reconnect if connection settings change
  - shutdown and restart if not configured to use external
- show a message in [p]play et al. when the connection hasn't been made
- move the JAR download to manager so audio.py can access it
- only start if no process exists
- bump red-lavalink to 0.2.3

Resolves #2306

redbot/cogs/audio/__init__.py

@@ -1,10 +1,8 @@
 from pathlib import Path
-from aiohttp import ClientSession
-import shutil
 import logging
 
 from .audio import Audio
-from .manager import start_lavalink_server
+from .manager import start_lavalink_server, maybe_download_lavalink
 from redbot.core import commands
 from redbot.core.data_manager import cog_data_path
 import redbot.core
@@ -22,30 +20,6 @@ APP_YML_FILE = LAVALINK_DOWNLOAD_DIR / "application.yml"
 BUNDLED_APP_YML_FILE = Path(__file__).parent / "data/application.yml"
 
 
-async def download_lavalink(session):
-    with LAVALINK_JAR_FILE.open(mode="wb") as f:
-        async with session.get(LAVALINK_DOWNLOAD_URL) as resp:
-            while True:
-                chunk = await resp.content.read(512)
-                if not chunk:
-                    break
-                f.write(chunk)
-
-
-async def maybe_download_lavalink(loop, cog):
-    jar_exists = LAVALINK_JAR_FILE.exists()
-    current_build = redbot.VersionInfo.from_json(await cog.config.current_version())
-
-    if not jar_exists or current_build < redbot.core.version_info:
-        log.info("Downloading Lavalink.jar")
-        LAVALINK_DOWNLOAD_DIR.mkdir(parents=True, exist_ok=True)
-        async with ClientSession(loop=loop) as session:
-            await download_lavalink(session)
-        await cog.config.current_version.set(redbot.core.version_info.to_json())
-
-    shutil.copyfile(str(BUNDLED_APP_YML_FILE), str(APP_YML_FILE))
-
-
 async def setup(bot: commands.Bot):
     cog = Audio(bot)
     if not await cog.config.use_external_lavalink():