Normalize CMake with cmakelint, 2-space indent

[mwtoews]

This PR does not change any functionality of CMake (or at least I hope not). It's intended to make these files more consistent, and using modern-ish CMake conventions. (This is only a small step towards #1263).

Most of these changes were found with cmakelint:

$ pip install cmakelint
$ git ls-files '*CMakeLists.txt' | xargs cmakelint
$ git ls-files '*.cmake' | xargs cmakelint

other changes are to try and use 2-space indents (this seem to be the norm), and spread file lists to 1-file-per-line, so possible changes are easier to see via diff.

[kbevers]

Thanks Mike. It's nice to get some consistency!