Big set of changes enabling the auto-generation of the GUI user function front ends.
This will create user function objects which are bound to the menu items, and the user function page
objects automatically from the user_function data object. The pipe user functions have been updated
to supply the needed data, and additional arguments have been added to the Uf_container.add_keyarg()
method. The Uf_container object can now accept additional wizard related variables.