Treat RightMouseClick as 'send to back'

[mmadia]

hrev44550

When Deskbar's application expander is open, a right mouse click on an individual item should be interpretted as send-to-back.

[axeld]

IIRC that's not so easy to achieve with menus, but I could imagine that we'll have a context menu there in the future, instead.

[leavengood]

Currently it does seem very difficult or impossible to determine if a menu item's Invoke() was due to the left or right mouse button (or whichever button.)

Maybe the Menu API could be extended in a backwards-compatible way to allow for asking how a menu item was invoked (keyboard, trigger, shortcut, mouse click with which button, programmatically, etc.)

Though Deskbar's use of menus is not the best anyhow, and it should probably be changed to use a new class for anything that isn't really a menu. The current ExpandoMenuBar is more of a tool bar. But such a change should really be part of a larger Deskbar redesign/rewrite, which might be better done after R1.