Focus Change Hooks

[justinDeu]

Add hooks to the Component trait that will be called when the Component gains and loses focus. These should be called inside the AppRouter on the different key binds which change the focused area.

[justinDeu]

AppRouter is a Component itself, so how would that work? The new functions can have default implementations that do nothing or should there be another, separate trait that only handles being focus-able that way the AppRouter doesn't have to worry about itself.