Switch to new WebIDE scanner / runtime API (bug 1069552)

Makes use of the new scanner / runtime API in WebIDE.

After this change, the add-on will still work with pre-API Firefox.

I've also added a Firefox for Android support, as it was helpful to build it to try out the runtime API.
I think we should just make the assumption that this module is going to be loaded only on 36+.
No need to try/catch, nor do any `if (Runtimes)`.
If would throw anyway on `type: Runtimes.RuntimeTypes.USB,`.