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.
mpd: Remove newline escaping code.

This was added for #881, where the correct fix turned out to be to remove
comments from the responses. We should still add some sanity checks for
verifying that our responses at the very least only contain printable chars.
Merge pull request #907 from adamcik/feature/mpd-remove-comments

Feature/mpd remove comments
docs: Add upmpdcli as an alternative to Rygel

Based on PR #871 by @woutervanwijk.

Fixes #871
Add appendinx about xbmc issues

XBMC won't boot because a different libtag version got
installed with mopidy system wide, and XBMC picks that up
insted of the one it vendors in. Added info how to fix this.
docs: Edit Raspbmc appendix a bit
Merge branch 'master' into release/v0.19.x
Merge branch 'release/v0.19.x' into develop
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
Merge branch 'release/v0.19.x' into develop

Conflicts:
	.mailmap
	AUTHORS
docs: Fix typo
startup: Log backend and frontend startup times.

Allows us to debug cases where a "bad" extension is blocking the startup.  In
there future we might also warning log extension that take longer than some
threshold to help find these cases.
http: Log errors instead of dying for HTTP startup.
http: Log errors instead of dying for HTTP startup.

(cherry picked from commit 9a2f8a3e4f5ea80ba0e6c497acfc8bee40a04375)

Conflicts:
	docs/changelog.rst
Merge branch 'release/v0.19.x' into develop
docs: Add :discuss: shortcut for linking to forum threads