* Refactored some of validator decorator to use clearer variable names internally.
* Validator decorator now supports treating arguments with default values as optional.
* controller.Notebooks.default() takes an optional note_id argument.
* controller.Notebooks.contents() takes an optional note_id argument.
* Wiki.js now makes use of these new controller APIs.
* Editor.js now takes a notebook_id argument to its constructor so it can properly make links.
* Made controller.Notebooks.save_note() return the newly minted revision timestamp upon a successful save.
* Whenever we get back a revision timestamp from save_note(), we store in in the client's list of revisions for that note.
* Now raising Access_error in controller.Notebooks in various places where the notebook requested is unknown.
* Tweaked pulldown CSS a bit. Now will sport a handy-dandy scrollbar if the pulldown gets too tall, at least in real browsers.
* Fixed bug where clicking "show on startup" checkbox directly didn't visually toggle the checkbox.
