Move ColorListView and ColorItem to shared in BPrivate namespace.
ColorItem typedef to BPrivate::BColorItem for apps that are already
using this class.
Gravity screensaver:
* ColorItem => BColorItem.
* Use make_color() to set colors.
Make color drop message name agnostic, check for B_RGB_COLOR_TYPE.
Add be:sender and source to drag message.
Add _SetTermColors() convenience method to set colors on all tabs.
Change-Id: I5a9f55d3ab423ccaa341997cf444603373024553
Reviewed-on: https://review.haiku-os.org/c/haiku/+/8846
Reviewed-by: John Scipione <jscipione@gmail.com>