Menu-accessible options to quickly adjust DDC contrast, RGB control availibility, defaults and scale

[waydabber]

DDC RGB black level and gain is not universally supported, and the style of support varies greatly among vendors. The way stuff works can be fine-tuned under Settings/Displays/Show DDC control settings, but since this is a common issue, it would be prudent to have some quick toggles in the DDC Video Adjustments section to quickly adjust things.

The following should be pre-set options:

• Default for RGB gain and black level: 50% or 100% (the are the common occurences)
• Default for contrast: 50%, 70%, 74%, 75%, 80%, 90%, 100% (the are the common occurences)
• DDC scale for RGB: 0-100, 0-200, 0-255 (for contrast the default 0-100 is almost always the case)

[waydabber]