Improve slider rendering

* Use a more appropriate thumb size
* Remove leftover debug red color
Don't use menulist for datalist color picker

* I can't figure out how to do this only for Haiku. The cpp tricks used
by IOS don't seem to work for us
* On Haiku, we always open a native color picker (which handles the
suggestions from the datalist directly), so there is no need for the
menulist appearance, which isn't working anyway.
Enable datalist support.
Bump version to 1.4.5.