Tiddlers that have a `draft.of` field are treated as pending drafts of the tiddler specified in the field. Draft tiddlers should also have a `draft.title` field that specifies the title that will be given to the tiddler when it is saved.
Several features work in concert to give the desired behaviour for draft tiddlers:
* The ListWidget can optionally render draft tiddlers through a different template
* The NavigatorWidget incorporates handlers for the following events:
** `tw-new-tiddler` for creating a new tiddler in draft mode
** `tw-edit-tiddler` for moving a tiddler into edit mode
** `tw-cancel-tiddler` for cancelling a tiddler out of edit mode
** `tw-save-tiddler` for saving a draft tiddler
* Draft tiddlers are automatically excluded from search operations
