Allow to list all files in project tree (especially for cmake projects)

I'm missing a the possibility to list all files in the project directory in the project tree. (Alternatively provide a hiercharchical tree view in the filesystem view).

Reason: cmake based projects often only list the related c++ files and not all the needed header files. QtCreator seems to list the mentioned c++ files and their corresponding header files, but header only implementations are hidden. Also other project related files (e.g. google protobuf) are not listed if they not directly assigned to a cmake target.
This makes it uncomfortable to use (existing) cmake based project with the QtCreator if the CMakeLists.txt files do not mention all files that shall be listed in the project view.