Handle notifications

[shanejonas]

Not sure how we'd handle this but would be nice to show the user notifications coming across the wire.

for metamask accountChanged for example is a notification that just comes across the wire.

also eth_subscribe kicks off notifications that come back with a notificationId via eth_subscription notification.

We need to handle these and show them to the user somehow.

[BelfordZ]

we can listen for window.ethereum.addListener('message') to receive events from eth_subscriptions. Its just a matter of where in the UI we should put these.