'Return a box with the main structure of the window. Looks like this:
|     TOOLBAR             |
|     TERMINAL     | SIDE |
|                  | BAR  |
|         LOG BOX         |
|        STATUSBAR        |'

def create_window_main_structure(self):

    scrollable_terminal = self.terminal.create_scrollable_terminal()
    terminal_event_box = self.create_event_box(scrollable_terminal)
    self.notebook = Gtk.Notebook()
    self.notebook.set_scrollable(True)
    self.notebook.append_page(terminal_event_box, Gtk.Label('1'))
    middle_pane = Gtk.Paned(orientation=Gtk.Orientation.HORIZONTAL)
    middle_pane.pack1(self.notebook, True, False)
    middle_pane.pack2(self.sidebar.box_it(), False, False)
    self.log_box = self.log.create_scrollable_logger()
    main_box = Gtk.Box(orientation=Gtk.Orientation.VERTICAL)
    main_box.pack_start(self.create_toolbar(), False, False, 0)
    main_box.pack_start(middle_pane, True, True, 0)
    main_box.pack_start(self.log_box, False, False, 0)
    main_box.pack_start(self.statusbar.mainBox, False, False, 0)
    return main_box
