Add screenshots to UI. Still need to implement resizing.

lib/roles/device/plugins/screenshot.js

@@ -47,10 +47,10 @@ module.exports = syrup.serial()
     router.on(wire.ScreenCaptureMessage, function(channel) {
       var reply = wireutil.reply(options.serial)
       plugin.capture()
-        .then(function(url) {
+        .then(function(file) {
           push.send([
             channel
-          , reply.okay(url)
+          , reply.okay('success', file)
           ])
         })
         .catch(function(err) {