FS-7508: change vpx encoder to not re-init the whole codec, it messes it up but side effect, we need to init the encoder at 4k and scale down to aovid the vpx resize seg

FS-7500: clean up logic of encoder flow and set rules on return values and tweak some codec settings on vp8

FS-7500: add video_decoded_echo var to make the echo app decode and re-encode video frames for testing

FS-7500: add SFF_USE_VIDEO_TIMESTAMP to tell video write frame if it needs to use a timer or not for timestamps

FS-7500: Work in progress.  Added codec config params that can be set from session and made vpx codec re-init on size change.  Also add periodic key frame timer

FS-7500: major refactoring pass.  Push concepts from mod_vlc as deep as possible and flesh out api to use everywhere else.  Round 2 will be to convert the bridge and other places using the same code

FS-7500: add support for codec control and use it to pass messages down to the codec and use it to implement keyframe reset for fir, pli and nack.  Later we will expand to handle nack correctly.

FS-7500: fix and use 32bit timestamp, frame->timestamp is defined as switch_size_t and not always 32bit

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