include cmake-modules manually instead

- Instead of using FetchContent
- Separate folder for easier update and for distintion
- LICENSE file included

cmake/cmake-modules/README.md

@@ -0,0 +1,5 @@
+The files in these folder were manually copy and pasted from the
+[cmake-modules repository](https://github.com/bilke/cmake-modules). It was decided to do
+this because only a small subset of its provided functions are needed.
+
+The license file in included here as well.