stream: always make stream dumping/capturing append to output file

Partially fixes #1393 (but not really).
command: stip path from playlist OSD display

But only if it's not e.g. a http URL.

Fixes #1388.
manpage: document new --stream-dump behavior

That's probably a good idea.
README: remove travis and coverity badges

Useless and ugly.
screenshots: set AVFrame parameters

Currently, libavcodec is rather lenient, but it might get stricter in
the future.

Fixes #1398.
cocoa: move the gl function loader to gl_cocoa.c
stream_pvr: sort channel list by --tv-channels order

Apparently this is what users would expect.

Going the way of least resistance (in terms of messing with this old,
rarely used code), sorting them by some kind of addition timestamp
(called priority in the patch) is the easiest.

Fixes #1390.