Add optimize settings button (this "replaces" the defaults button when available)

Displaying both the defaults and the optimize button requires (currently
unnecessary) tweaking of the settings dialog, so they are mutually exclusive for
now
Implement optimize settings button for publish settings

This includes "optimizations" for almost all publish warnings; the aspect ratio
warning is not fixed because trying to fix that has wider repercussions for
scene/source layout/positioning and potentially even required bitrate

A possible future "optimization" to fix the aspect ratio warning would be to
compute a number of possible choices based on the current downscale setting with
a target output resolution of 480p/540p/720p/etc. and let the user select one of
the resulting base resolutions