command: add osd-sym-cc property

This allows you to reproduce the OSD symbol.
command: allow using ASS tags on OSD messages

We don't allow this by default, because it would be silly if random
external data (like filenames or file tags) could accidentally trigger
them.

Add a property that magically disables this ASS tag escaping.

Note that malicious input could still disable ASS tag escaping by
itself. This would be annoying but harmless.
player: allow overriding OSD message for all OSD levels

Until now, you could override only level 3 with --osd-status-msg. Extend
this, add add --osd-msg1 to --osd-msg3 (one for each OSD level). OSD
level 0 always means disable OSD, so that isn't included.

--osd-msg3 corresponds to --osd-status-msg, but they're not exactly the
same. To allow more customization, --osd-msgN do not include the OSD
symbol. The symbol can be manually added with "${osd-sym-cc}". We keep
the "old" option for some short-term compatibility.

--osd-msg1 should be particularly useful; for example you could do:

    --osd-msg1='${?pause==yes:${osd-sym-cc}}'

to display a "paused" symbol when paused, and nothing during normal
playback. (Although admittedly, the syntax is quite a bit of work.)