Add JS companion app

This PR adds JS code, which runs in the official Pebble app, and therefore removes the need for iOS companion app.

The JS code runs both on iOS and Android and since iOS 8, the Pebble app does not need to be in foreground. As long as the Pebble watch is connected to the official Pebble app, the JS code runs whenever it's needed (when the watch requests it).

The preferences (which can be open from the Pebble app) are hosted at http://pebciti.tomasvitek.com/preferences.