UI Key Locking

This adds locking and session support to the UI, specifically:

- View if a key is locked, and what session is locking it
- Disables forms and buttons for locked keys
- Lists sessions on a node and gives you an "invalidation" button to kill the session.

Here's a GIF:

![foo](https://cloud.githubusercontent.com/assets/846194/3204838/a70b8442-edae-11e3-8ea9-f918ef3e3746.gif)

It also improved right column scrolling.