player: reset playback-related fields right on start
command: disable some commands/properties properly in idle mode

In particular, don't allow to add any external subtitle tracks in idle
mode. This make no sense and would just lead to leaks or worse.
command: make m_property_strdup_ro with NULL mean unavailable

This catches a few cases which basically call:

    m_property_strdup_ro(..., ..., NULL)

which would return NULL strings. This should generally be avoided
(although it's allowed due to reasons), and it seems most callers
actually intend this to mean M_PROPERTY_UNAVAILABLE.
demux: get rid of old wrapper

demux_info_get() used to be central, but was turned into a wrapper, and
now there was only one caller left. Get rid of it.
command: remove broken quvi-format property

Never really worked, and libquvi is probably a lost cause anyway.
player: simplistic HLS bitrate selection

--hls-bitrate=min/max lets you select the min or max bitrate. That's it.
Something more sophisticated might be possible, but is probably not even
worth the effort.
player: show HLS bitrate as fallback for track titles

HLS streams as demuxed by libavformat have no track title metadata. So
show the HLS bitrate if no title is set. Could be useless or annoying,
so it's a bit controversial, I guess.
player: add --osd-playing-msg option