Add option to use folder as topic / #6460

I recently encountered problems with structuring the documentation of large projects. Normally our workflow is this:

1. Create a task
2. write precise specification
3. Implement Task or create turn Task into Folder and add Subtasks
4. If Task is implemented, turn into Topic if its description is useful for project documentation.

However, if the Task was turned into a Folder with Subtasks only, we cannot use the folder´s description as documentation. It will only be listed in the Documentation tree, if it contains further Topics. To encounter this problem I propose to add a display option which will be called something like...

• "Show folder as topic"
• "Use folder for documentation"
• "List in documation"
• "List folder as documentation topic"

The implementation will be easy (add an additional check to the creation of documentation list). To keep the documentation tree clean, the default value for this feature will be OFF.