add and use event bus for UI progress

internal/bus/bus.go

@@ -0,0 +1,19 @@
+package bus
+
+import "github.com/wagoodman/go-partybus"
+
+var publisher partybus.Publisher
+var active bool
+
+func SetPublisher(p partybus.Publisher) {
+	publisher = p
+	if p != nil {
+		active = true
+	}
+}
+
+func Publish(event partybus.Event) {
+	if active {
+		publisher.Publish(event)
+	}
+}