With public ImageOp fields there was no way to mark an image.Image as modified.
Replace them with NewImageOp that always make a copy, and use the opportunity
to ensure the copy is ready to upload to a GPU texture.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Package ui is now only about units except for the Config.Now method.
Remove Now and rename Config to Converter. Add layout.Config to
replace the old ui.Config.
Signed-off-by: Elias Naur <mail@eliasnaur.com>