Move the main window out of MainMenu.xib into a document window owned by a window controller, so that each document opens in its own window.
* Document.j: Add a CPDocument subclass that creates a DocumentWindowController for each document.
* DocumentWindowController.j: Add a CPWindowController subclass that loads DocumentWindow.cib and sets itself as the window's delegate.
* Resources/DocumentWindow.xib, Resources/DocumentWindow.cib: Add the document window, with DocumentWindowController as File's Owner.
* Resources/MainMenu.xib, Resources/MainMenu.cib: Remove the window, name the application menu Text Editor, rename Preferences to Settings, and remove Quit.
* AppController.j: Remove the window outlet and the code that made the window fill the browser.
* main.j: Import Document.j.
* Info.plist: Declare the Document type with Document as its document class.
