The license type.
Allows to set the application's license froma list of known licenses.
If the application's license is not in the list, [property@AboutWindow:license] can be used instead. The license type will be automatically set to `GTK_LICENSE_CUSTOM` in that case.
If set to `GTK_LICENSE_UNKNOWN`, no information will be displayed.
If the license type is different from `GTK_LICENSE_CUSTOM`. [property@AboutWindow:license] will be cleared out.
The license description will be displayed on the Legal page, below the copyright information.
[[email protected]_legal_section] can be used to add license information for the application dependencies or other components.