[FEATURE] Partition support #609

Is your feature request related to a problem? Please describe.
No, unless a problem is a feature supported by ncmpc but not ncmpcpp

Describe the solution you'd like
That the ncmpcpp add the code to support interacting with a partition different from the original (possibly even adding a move output feature)

Describe alternatives you've considered
Making my own mpd "server" that gets given the partition to show at, and will let the connecting program interact with that partition only, by restricting the change of partition, (this way I could connect ncmpcpp to a different address and get to be able to modify a partition that's not the default.

Additional context
https://github.com/MusicPlayerDaemon/MPD/blob/master/doc/protocol.rst#partition-commands