User preferences: Use checkbox for Cycles device selection
User preferences: Use checkbox for Cycles device selection

It was totally unclear whether the device is enabled or disabled.
Lots of people got fully lost in the current interface.

While the solution is not fully ideal, it is at least solves
ambiguity in the interface.

tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird,tangent-opensource/coreBlackbird