build: Beautify cmake files

build: Beautify cmake files

Add .cmake-format.py
Add cmake-format docs to CONTRIBUTING.md
Minor edits to existing files

Due to a bug in cmake-format, use this script to reformat:

for i in CMakeLists.txt cube/CMakeLists.txt cube/macOS/cube/cube.cmake cube/macOS/cubepp/cubepp.cmake icd/CMakeLists.txt mac_common.cmake vulkaninfo/CMakeLists.txt vulkaninfo/macOS/vulkaninfo.cmake
do
    sed --in-place='' 's/^  *#/#/' $i
    cmake-format --in-place $i
done

Change-Id: Ie451aacd7402828ad4d62adc04048449d0ea2abe