Add panel toggles to View menu

[matterhorn103]

Currently, panels (and toolbars) can be hidden or made visible only by right-clicking on the toolbars or on the header of a panel to open a small menu. This works fine but is non-obvious and hard to discover, leading possibly to frustration if a panel is closed accidentally.

It would be a good idea to add the panels to the View menu, perhaps as a sub-menu under View|Layout, or under two separate sub-menus for View|Toolbars and View|Panes.