Add support for content-based presets

[kmcclive]

Per @docgonzo2015 on issue #112:

There are a few more options in Video Codec that belong as a base: the standard stuff for different film sources. For example 2018 action movies need different settings than a Belmondo movie from the 70s. There is virtually a basic preset that is customized with a few options. Fog is very helpful to set intra high. Comics it goes high with b-frames.

Examples:

• Grainy Movie: deblock -1:-1, nr-intra 400, nr-inter 400
• Cartoon Movie: ref 6, bframes 16, aq-strenghgt 0.6
• Documentation : qcomp=0.7, frame-threads 2, merange 48
• Concert : copy audio