Added JSTorrent Browser Extension to the externally_connectable manifest key

See http://developer.chrome.com/extensions/manifest/externally_connectable.html for more about the `externally_connectable` key. i think this is the right approach here.

In the mean time, you may want to update your Browser Extension to use Event Pages instead of background so that your extension doesn't consume memory for nothing. See https://developer.chrome.com/extensions/samples.html#context-menus-sample-(with-event-page) for an example.