Installs the GtkEditable properties for
This is a helper function that should be called in class_init, after installing your own properties.
To handle the properties in your set_property and get_property functions, you can either use
delegate_get_property (if you are using a delegate), or
first_prop offset and add it to the values in the
EditableProperties enumeration to get the property IDs for these properties.
property ID to use for the first property
the number of properties that were installed