Add GCM downstream to device for sending texts and info back to device

[YeomansIII]

Using an open socket to Firebase is not battery efficient at all. Google Cloud Messaging exists for this purpose, to send downstream messages to devices. I've tested client to client GCM on the 'gcm' branches, but it doesn't seem possible. One solution would be to have a GCM 'server' running in the chrome extension. But that would add to the setup process and require users to make a project on the Google developer dashboard.