some toolbar fixes

some toolbar fixes

* tweak "GUI: Button Bar" org unit setting to accept either the label or
  id for an existing toolbar, and have it actually work when a window is
  opened
* expose hard-coded toolbar layout option as a Default menu entry

If the open-ils.menu.toolbar preference or ui.general.button_bar org unit
setting references a non-existent toolbar, then a hard-coded stock toolbar
will render.  However, the menu entry 'None' will be selected under the
Admin -> Workstation Administration -> Toolbars -> Current menu, which is
confusing.

With this change, a Default menu entry will be selected whenever the hard-
coded layout has cause to render, and you can also explicitly select that
menu entry to use the default and save it as your workstation default.

Signed-off-by: Jason Etheridge <jason@esilibrary.com>