Wording on the UI, slider consistency and material mask switches layout.
Reviewed By: Sebastian Parborg (zeddb)
Differential Revision: http://developer.blender.org/D11839
This replaces header include guards with `#pragma once`.
A couple of include guards are not removed yet (e.g. `__RNA_TYPES_H__`),
because they are used in other places.
This patch has been generated by P1561 followed by `make format`.
Differential Revision: https://developer.blender.org/D8466