Warn about files on the file system that are not part of the project

Warn about files on the file system that are not part of the project.

If a file is not part of the project it will not be added to the cmake files.
At least for known file endings we should warn about this, since this is likely to be a bug.

Whenever we generate the cmakfiles.txt and we find e.g. QML files not part of the project we should warn.

Endings we should check for:

.qml, .js., .json, .png, .jpg, .mesh .hdr, ktx, qsb, .glsl;.glslv;.glslf;.vsh;.fsh;.vert;*.frag, mp3, wav, ttf, otf., qad.