Menu creation widgets

These can be considered another specialized form of Layout widget for the creation of Menu components.

MenuBars, MenuPanes, MenuButtons, and ToggleButtons are created as follows:

       MenuBar                ->->->  VtMenuBar
           MenuPane           ->->->      VtPulldown
               Buttons        ->->->          VtPushButton
               Separators     ->->->          VtSeparator
               ToggleButtons  ->->->          VtToggleButton
           ToolButtons        ->->->      VtPushButton

VtMenuBar(VTCL)

Creates a MenuBar container. The menu bar is populated by creating VtPulldown children (for pulldown menus) or VtPushButton children (for toolbars).

VtPulldown(VTCL)

A PullDown is a container for a menu panel that pops up from a button. VtPulldown creates both the button and MenuPane container.

Pulldowns can be parented only by MenuBars, other PullDowns or Popups.

The button created will be named PullDownName_vt_button.