Initial Commit of FFMPEG settings.

[odgrace]

Current behavior for ffmpeg settings is to set crf=0 and b:v 40M which I understand are mutually exclusive. They also have no effect for some hw accelerated options like videotoolbox. The approach taken is to set some sane defaults per encoder that will grow over time so must users can just press a button and have it 'work'. The settings are not set in stone at all and are not comprehensive at this stage.

The method Utils.load_encoder_defaults_yaml attempts to find this settings file but falls back to the existing encoder settings. If no settings around found it will also fall back to those same defaults, whether or not they work for the specified codec.

Keen to get your feedback to see if this is a direction worth taking. A few things im thinking of:

1. I don't know if this will impact the GUI. I still have to try and get the GUI working but I'm caught up in the attrdict problem
2. I've used yaml to allow the specification of encoder parameters but this adds a dependency. Open to other options if this is a problem
3. We still have the same issue of encoder_settings going from resources to root when packaging the GUI, just like font.ttf