Several small fixes and better artist parsing

This makes the song title and artist required tags and treats them special. There should only be a single title and the artist can be broken up automatically based on separators like "feat.", "and", slashes and ampersands. The original string is retained so it can be shown when we want everything all together.

Other small fixes:

• When we select a player exclusively, we weren't properly disconnecting other players so other players might play as well, but not be synced properly.
• Updated a renamed experimental feature (drain_filter -> extract_if)
• Fixed a new clippy warning for Arcs
• Allow thumb.jpg as well as cover.jpg
• Speed up background song and tag list downloading
• Only update the metadata when it changes to reduce downloading of thumbnail on Windows