Bug 998328 - Add a remote debugging status icon. r=21

![screenshot](https://cloud.githubusercontent.com/assets/599268/4887774/a9f5fe40-6387-11e4-90c4-81393243cc75.png)

The icon comes from the gaia-icons font: https://github.com/mozilla-b2g/gaia/blob/master/shared/elements/gaia-icons/gaia-icons.css#L15