rawvideo: Fix timestamps & input options

demux:
 - Use accurate timestamps (date_t)
 - Signal frame rate in fmt_out
 - Fix aspect ratio for YUV4MPEG2
 - Reoganise input options to allow sensible overrides
   Ie: extension gussing < yuv4mpeg < cmdline

codec/packetizer:
 - Fix incorrect assumption of 25 fps video
 - Use accurate timestamps (date_t)
 - Copy input format as output format (to preserve frame rate)
 - Set progressive flag per picture

TODO:
 - Have module option for interlaced
 - Detect interlaced in demux for YUV4MPEG2
 - Have codec read set the interlaced flags in the video
 All seems rather tricky for the moment (well, YUV4MPEG2 bit does,
 since the demuxer strips the headers that reveal the interlace
 mode).

Signed-off-by: David Flynn <davidf@rd.bbc.co.uk>
Signed-off-by: Laurent Aimar <fenrir@videolan.org>