app: remove the image's "Enable Color Management" toggle
It was not doing anything right since space invasion. We now treat the built-in sRGB profile like any other profile and never bypass conversions based on some weird toggle. Instead, introduce a "Use sRGB Profile" toggle which, when enabled, hides whatever profile away so the image actually uses the built-in sRGB profile. This is different from discarding and then re-assigning the same profile only by being faster and more convenient.