Add autoclosing feature for browser tabs


![pr](https://cloud.githubusercontent.com/assets/2142829/5423690/9698497c-82ca-11e4-9b1a-39a24285c099.gif)
Close the tab on `kill`.
`kill` is triggered when the livedown server shuts down.
sure, check this [stackoverflow answer](http://stackoverflow.com/a/19768082/726020). in short, the workaround I have provided is better than using plain `window.close()` since some browsers will not allow closing of a window not opened by that script. we then *fake* the opening to be able to close it. this will probably also not work in the future, but meh, still better than just `window.close()`.