[abusch]

Makes live radio streams (e.g. franceinfo) usable: they couldn't be paused, and the player said "Nothing playing".

• Stop: streams that can't be paused can now be stopped with Space. Sonos has no stop command, but pausing such a stream stops it.
• Station: when a stream has no current track, what it says it plays is shown instead (or the station's name), with the station's logo and no elapsed time, like the Sonos app. This upgrades sinuous-client to 0.4.0, which decodes it.
• Stopped groups: idle groups, e.g. a stopped stream, show a stop icon instead of the pause one, and the group panel tells stopped and paused groups apart.
• Buffering: groups that are buffering say so, in the group panel and instead of the progress bar.

Fixes #179