Moves the preset into a menu for the panel header, so it can be changed
without opening the panel and takes up less space. Two remaining issues:
* For long lists the add new preset button can be scrolled off screen.
* We should support showing the name of the chosen preset in the panel
header, but the current preset system does not support detecting which
preset is used.
Differential Revision: https://developer.blender.org/D3366
7a10cfe7fe