Actually bubble errors to user

[OxygenCobalt]

Long-term effort to remove all instances where Auxio doesn't indicate an error to the user and just logs a message. It's an extreme hassle to debug and makes managing issues a nightmare when I have to hand-hold people in making bug reports.

• Indicate errors during playlist import
• Indicate when the music loader has to "compromise" or otherwise indicate that it's going to act weird (possibly useful with Clearly indicate when Auxio is using sort names #612 and Tolerate inconsistent MusicBrainz ID usage #555)
• Indicate errors during playback restore and general playback

This is a little complicated since it requires me to begin using Snackbar components, which means another thing to cram in my brittle main UI.