gobject: Add install_properties()

Since we added g_object_notify_by_pspec(), an efficient way to install
and notify properties relies on storing the GParamSpec pointers inside
a static arrays, like we do for signal identifiers.

Instead of multiple calls to g_object_class_install_property(), we
should have a single function to take the static array of GParamSpecs
and iterate it.

https://bugzilla.gnome.org/show_bug.cgi?id=626919

Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>

docs/reference/gobject/gobject-sections.txt

@@ -244,6 +244,7 @@ G_OBJECT_TYPE_NAME
 G_OBJECT_CLASS_TYPE
 G_OBJECT_CLASS_NAME
 g_object_class_install_property
+g_object_class_install_properties
 g_object_class_find_property
 g_object_class_list_properties
 g_object_class_override_property