mpd: optionally enable opus support

Closes #31316.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
imapsync 1.592

Closes #31325.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
imapsync: simplify resource installation
Signing Party 1.1.7 is no longer available.

Use 1.1.8 instead.
mpd: update 0.18.12 bottle.
signing-party: add 1.1.8 bottle.