'Attach to the notebok the workspace sidebar and the host_sidebar'

def __init__(self, workspace_sidebar, hosts_sidebar):

    super(Gtk.Notebook, self).__init__()
    self.workspace_sidebar = workspace_sidebar
    self.hosts_sidebar = hosts_sidebar
    self.set_tab_pos(Gtk.PositionType.BOTTOM)
    self.append_page(self.workspace_sidebar, Gtk.Label('Workspaces'))
    self.append_page(self.hosts_sidebar, Gtk.Label('Hosts'))
