Added audio downloading, switched to yt-dlp

- enabling and disabling mods using config.json works now
- switched to yt-dlp (it supports YouTube without problems)
- added audio downloading
- changed 'mvd' mod tag to 'md'
- added filesize in qualities list
- changed thumbnail size 280x280 at most
- .webm and .mhtml extensions are ignored now
- fixed encoding errors in utils.get_md5 (they are ignored now, so not an actual fix, but it 100% won't break anythink)

hubot.py

@@ -94,6 +94,11 @@ async def _cb_new_message(event) -> None:
     tasks = []
     # pass the event to all mods interested in it
     for mod_name in _mods:
+        # mod is not enabled for this user?
+        if mod_name not in sessions[name]['config']['accounts'][name]:
+            continue
+        if not sessions[name]['config']['accounts'][name][mod_name]:
+            continue
         # mod
         mod = _mods[mod_name]
         try: