Completely disable keyboard light

Options
1. Disable keyboard light completely. I cannot be changed except cli like `defaults write`.
  * no idea
2. Disable `Adjust keyboard brightness in low light` (below), minimize brightness, and remove icons from touchbar.

<img width="780" alt="image" src="https://user-images.githubusercontent.com/4200911/46915535-fafbc880-cfe7-11e8-9acb-ec67dd8fd8f5.png">
