The crash fix is to always create a new project (done in method ProjectManager::newProject())

Furthermore NewProjectDialog distinguishes now between "create" and "save", since  otherwise it would look ugly on the UI. Imagine these steps:

Open BA, edit something, click "create new project". Now first a dialog for saving is shown, then a dialog for creating. Without the done changes, two dialogs with title "Create project" would show up.

As recommended by
https://google.github.io/styleguide/cppguide.html#The__define_Guard

Correct .h file header comments: "Declares" -> "Defines". Also remove include comment "inheriting from". This resolves #1550.

Made include guards uniform, using the command sc-intern/edit-scripts/update-include-guards.py Core Fit GUI/coregui GUI/crashhandler/

Refactoring in ProjectDocument to be able to open project files from any directory (before name of directory had to coincide with project file name)