Added some notes and deleted some dead code

Stopped setting tabIndex=-1 on click eater. On right-click in Chrome, light dismiss
would trigger due to focus moving to click eater. This didn't happen in IE
because preventDefault in pointer down prevented focus from moving. This change
prevents the inconsistent behavior. Now right click doesn't dismiss in IE or
Chrome. However, the original design was for right-click to dismiss.
Hook up escape key to service
Delete dead focus code from AppBar & Overlay