The properties window can be used from within Nautilus, and therefore a
dialog window makes sense, or from outside Nautilus, such as the
FileManager dbus free desktop standard.

In the later, used for integration with things like desktop icons
extensions, we need to keep the application alive since GApplication
would close the application if no application window is alive after a
timeout.

To fix this, this work makes the window hint a regular window if used
from those cases.