(pre) release 0.17.0-rc2

Adds support for "mirroring" playback to another device (select it in the settings). This allows (for example) simultaneous playback through both the headphone port (whatever is plugged in) and the builtin speakers.

The main purpose of this is to play music through a loopback device together with the main output, and perform further actions on that loopback device. Loopback devices are sold separately.

known issues:

• the current song is not actually replaced if you press 'play' from the search, if the player is paused.