Blender Git Commit Log

UI: Simple confirm dialog when loading new file

I also had to make the "New" operator a submenu in the
`File Context Menu`, so that you can still select the template.

This partially solves T61599. Currently the confirm dialog
is not shown when an already existing file is opened.
Implementing that requires a bit more work and will be
done in a separate patch.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D4732