When a new project is created, the "New Project" dialog should provide an option to copy the list of open files from the current project.

Usually I find myself opening files that are not actually relevant to the currently active project, until I decide that all those files belong to a different "topic" and decide to move them to a new Geany project. The simplest way to do this is to just "clone" the project, and then close the files that are not relevant in both old and new project. Unfortunately, Geany doesn't have a "clone" or "save project as" feature (as suggested in #2206), so I have to manually copy the `.geany` project file, rename it, open it with my *second* favorite editor (can't open it with Geany) and edit the name and base path, and then proceed to close the unneeded files. Having an option to "clone" the project (either through a "Save project as" menu entry as proposed in #2206 or through a "Keep files from current project" checkbox in the "New Project" menu) would simplify this.