Expose Mutable classes in python bindings

Since the default classes have no really usable public constructor any
longer, exposing the Mutable classes for python makes more sense.

python/templates/selection.xml.jinja2

@@ -29,7 +29,7 @@
 {# Otherwise the python interface does not work in gcc builds #}
 {# Additionally, in order to allow "direct" access to the user facing classes #}
 {# we have to declare them here, otherwise they cannot be easily imported #}
-{{ class_selection(class) }}
+{{ class_selection(class, prefix='Mutable') }}
 {{ class_selection(class, postfix='Collection') }}
 {% endfor %}