refactor(event): align serialization properties with the rest

[Arqu]

Event's are breaking out of our default pattern for naming fields when serialized. However due to a lot of these events being user and/or stored elsewhere we need to be able to deserialize either for backwards compatibility.

Fixes #1989

[ramfox]

There is one other place we should consider changing:

qri/lib/websocket/websocket.go

Lines 106 to 114 in e499860

	func (h *connections) messageHandler(_ context.Context, e event.Event) error {
	ctx := context.Background()
	evt := map[string]interface{}{
	"type": string(e.Type),
	"ts": e.Timestamp,
	"sessionID": e.SessionID,
	"data": e.Payload,
	}

This is how we serialize events over the websockets. I'm proposing we change these to match the way we serialize our other events (namely, change "ts" => "timestamp" & "data" => "payload"), that way all our event serialization uses the same fields. This will force a refactor on frontend (@chriswhong @boandriy), but I think it will be better in the long run.

[Arqu]

Agree with Kasey here, we should continue the same naming conventions to frontend as are on the back end.
I'll ping/file and issue on frontend to align this and make sure it lands at the same time.

[Arqu]

I went ahead and did it solo, but unsure if I caught it all or if this is good at all.
qri-io/frontend#645