Refactoring #2466

Updated by wuttke 5 months ago

Instead of
#include "SessionItem.h"
we'll have
#include "GUI/coregui/Models/SessionItem.h"

This is recommended by, and how we do it in other projects.

* Provides valuable information to the reader of the code.
* File names must be no longer unique. This allows in some cases for shorter or more natural names.
* Slight simplification of CMake code.
* Conformity with our other projects.

* Renaming files requires more typing, or use of a script.

The required script mv-src is available in