[Catalyst] finalize actions

[Perrin Harkins]

The finalize actions (or methods, or whatever) could use more
documentation.  They are only briefly mentioned in Manual::Internals and
Engine, which makes it hard to understand how the FillInForm plugin is
supposed to be used.  Or maybe this just means that FillInForm needs
better docs, since you wouldn't normally use finalize in your app, but
you do  need to understand that the finalize method in that plugin is
going to get automatically called by Catalyst.

- Perrin