Improved documentation for coreComponents packages

[paloma-martinez]

What needs to be documented?
Many coreComponents packages such as codingUtilities, common, etc.. seems to not be documented on what they contain, manage, should not contain. As a developper, it is currently not obvious the responsibilities of some of these packages.

What sort of documentation would help?
DevGuide doc.

What are the deficiencies of the existing documentation?
The files and classes are documented but the containing packages lack description.

Additional notes or context
In addition, it might be very useful to have a small documentation at the top of each CMakeLists.txt file such that brief info about the package is accessible easily, especially while making modification in the package.