FS-7513: add profile param video-no-video-avatar and variable video_avatar_png to set video replacement avatar images
add also video_no_video_avatar_png to only check the var on no-video situations

FS-7512: add mod_png to play a png as video defaults to 10 sec add {png_ms=N} to change (negative number is forever)

don't start playing until the first read in vlc vid handles
use correct buffer len
Fixing typo. memset should zero out the whole struct
add some mutexes
fix locking issue on bad formatted input string

FS-7513: Add new conference profile param video-mode (mux,transcode,passthrough) with passthrough as default
remove transcode-video, decode-video, mix-video flags