mpd: Enable browsing of empty dirs

This was disabled together with a bunch of other changes without any
explanation in commit f24ca36e5a5b72c886d6d8e8df88be79fb094dda. I'm
guessing that this wasn't intentional, and no test covered the case.

(cherry picked from commit 4e508cd01750bcef9e0e9c7b70798eacd276aef8)
mpd: Remove "Comment" tag type from translator output.

Newer versions of the protocol have removed this tag, so we should as well.
This also works around the issue of #881 which was breaking things with
newlines in comment fields.

The readcomments command seems to replace this, but it seems to only care about
specific extra tagtypes, not the general comment tag we normally collect when
scanning things.

(cherry picked from commit 08a8d5c43be271a41af74ce0c7df9d871cf2b532)
[local] fix modified files not being updated

(cherry picked from commit dfd897832a952c4a7da655f504dc0c162433c539)
docs: Update changelog
docs: Update authors