Allow nested Flyouts
Remove dead function createClickEatingDivTemplate
Basic integration of AppBar w/ LightDismissService

- AppBar hides on tap
- AppBar hides when it loses focus

Doesn't play well with other AppBars. Also, doesn't restore focus properly
after Flyout opens on top of it.
AppBars talk to AppBarManager instead of service

Now the AppBars play together a bit better (they share a zIndex so you can
interact with 2 AppBars at the same time and you can move focus between
them without causing other AppBars to dismiss).