Built-in browser

This is probably still a bit far out there, in terms of priorities for the next few releases, but in the long term, it would be really nice to have a built-in browser. My particular use case is the [Jupyter Notebook](http://jupyter.org). This goes very much hand-in-hand with #142, since the notebook server I'd be connecting to is only reachable via SSH tunneling (this is a very common setup).

My recommended UI for this would be a "browse" command, as in `browse https://localhost:8888` that would open the URL in a new tab (with terminal and browser tabs being intermixed, so that I can swipe left and right to switch between them).

Having a terminal, port forwarding, and the notebook all in the same app would be an absolute powerhouse, and would allow to do some very real science on the iPad (this is me talking as a physicist, but I think data science and machine learning uses very similar workflows, and everybody and their dog is doing that these days). Web devs would probably also use this feature.

It would put Blink very far ahead of the competition. [Coda](https://panic.com/coda/) in particular already has the combination of terminal and browser, but no port forwarding. That means that I need to run another application ([vSSH](http://www.velestar.com/Pages/VSSHIOSPage.aspx)) in the background just for the port forwarding, and switch back to it every 10 minutes so that iOS won't kill the connection - quite annoying. Blink also has a far cleaner and snappier interface than Coda at this time, as well as better font rendering.

Start with the proposed `browse https://localhost:8888` command and the terminal/tab behavior described in the issue; no implementation files or tests are named. Done would mean an in-app browser tab can open a URL alongside terminal tabs and support the SSH-tunneled notebook workflow.

Written by the indexing model from the issue text.