Webkat

**Not ready to merge**

Here are some things that are left to do before we can add this to master:

- [ ] Decide if Java bindings goes in the initial commit? I say let's do it. @jnfoster, thoughts?
- [ ] Let the current `update` URL take pure NetKAT in the body
- [ ] Create `update_json` URL with pure JSON encoding
- [ ] Demo applications? We have two forwarding applications (learning.py and repeater.py). It doesn't make sense to run them simultaneously. Let's add a silly monitoring application to truly demo this system.