Slate: add a couple of focus bindings
Slate: add a couple of focus bindings

Not sure how much I'll use these, as they don't feel as easy as a simple
Command-Tab, but let's give it a shot.

Signed-off-by: Wincent Colaiuta <c76ac2e9cd86441713c7dfae92c451f3e6d17fdc@wincent.com>

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent