* model.Note has a deleted_from member to indicate the notebook id it was deleted from (if any)
* controller.Notebooks sets the deleted_from member and makes all deleted notes startup notes in the trash
* new controller.Notebooks.undelete_note() method
* split up the idea of UI messages into errors and informational messages, with separate CSS
* updated Editor and Wiki UI code to deal with new deleted_from variable
* added "undelete" button when viewing a deleted note, and "delete" changes to "delete forever"
* added a "trash" link to the notebook links
* reorganized responsibilities for displaying notebook/user links among Wiki.populate() and Wiki.display_user()
* when deleting messages in a notebook with a trash, displaying "The note has been moved to the trash"...
with a working undo button!
* tweaked focusing logic in display_search_results(), which has been renamed to display_loaded_notes()
* Made sure the trash is not exposed by the read-only notebook view.
* Modified model.User.check_access() to consider read-write access to a
notebook to be sufficient for access to that notebook's trash.
* Modified controller.Users so new users are created with a notebook that
has a trash.
* Changed controller.Notebooks so deleted notes go to the trash (if any).
* 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.
