Record next step events for tutorials to help understand progress

src/reducers/cards.js

+import analytics from '../lib/analytics';
+
 import decks from '../lib/libraries/decks/index.jsx';
 
 const CLOSE_CARDS = 'scratch-gui/cards/CLOSE_CARDS';
@@ -38,6 +40,11 @@ const reducer = function (state, action) {
         });
     case NEXT_STEP:
         if (state.activeDeckId !== null) {
+            analytics.event({
+                category: 'how-to',
+                action: 'next step',
+                label: `${state.activeDeckId} - ${state.step}`
+            });
             return Object.assign({}, state, {
                 step: state.step + 1
             });