FS-7513: let the core thread to read video if vid-floor in conference already locked-hold by someone else

It by default remains the default behaviour

However, you can setup a relationship between members to let the
member choose to see anyone else but the floor, e.g.:

  conference 3000 relate 1 2 sendvideo

In the above command member 2 will see member 1's video regardless
member 1 has video floor or not

the callback will be called on each loop on read video frame, or
the callback function call run it's own loop to take over the core
loop so it can read video from session by itself.

the callback function can -

return SWITCH_STATUS_SUCCESS to wait another loop
return SWITCH_STATUS_CONTINUE to continue use the default behaviour
return anything else will break the core video loop and end the
       core thread

added switch_core_codec_encode_video and switch_core_codec_decode video and add separate video implementations
the switch_core_video code depends on libvpx, wraped into the switch_ namespace like switch_apr, need to figure out how to find the correct libvpx lib in autotools

the autoconf portion to detect the correct location of libopenh264

Basic conversion for vpx too.
Borrowing from ldns handling, setup mod_vpx to prompt for the required library when the module is enabled

FS-7502: add simple video media bug implementation, should work with .fsv, be sure to set enable_file_write_buffering=false

Conflicts:
	src/include/switch_types.h

conference 3000 record /tmp/testrecord.fsv
call 9194 try to playback
mp4 should also work with the mp4 file format, will be available soon

FS-7582 #resolve #comment port from 1.6 its probably better to start working on 1.6 for any webrtc or dtls stuff