fix windows build, add exit from app menu

[jafrado]

No description provided.

[jafrado]

@MarkMuth - please have a look, I added rendering the image in the dataset as well as changing the view on the 3D Point cloud. You'll find this very useful for testing. Of course I also fixed the Windows build (added usleep).

[MarkMuth]

@jafrado Thanks for your interest in this project. I would very much like to merge your changes, but I see two problems here:

1. Your Pull Request looks like it's not based on the latest version of the master branch.
2. The fix for Windows seems to break the Linux build. I recommend to open a second PR for the Windows build and would like to have it in a separate branch as long as compiling for Windows and Linux is not possible from the same branch. Since I cannot test the Windows build myself, I would also like you to provide build instructions in the documentation directory as was done for Ubuntu 20.04.