Step Builder: Lock and unlock navigation when appropriate.

When navigation is locked, it is not possible to click arrow buttons to
navigate between existing units. This should be the case during
completion of an attempt.

When navigation is unlocked, users can click arrow buttons to navigate
between existing units. This should be the case when user has completed
an attempt, i.e., when they are reviewing their grade for the last
attempt.

problem_builder/public/js/mentoring_with_steps.js

@@ -178,6 +178,11 @@ function MentoringWithStepsBlock(runtime, element) {
     function updateDisplay() {
         cleanAll();
         if (atReviewStep()) {
+            // Tell supporting runtimes to enable navigation between units;
+            // user is currently not in the middle of an attempt
+            // so it makes sense for them to be able to leave the current unit by clicking arrow buttons
+            notify('navigation', {state: 'unlock'});
+
             showReviewStep();
             showAttempts();
         } else {
@@ -324,6 +329,11 @@ function MentoringWithStepsBlock(runtime, element) {
     }
 
     function showGrade() {
+        // Tell supporting runtimes to enable navigation between units;
+        // user is currently not in the middle of an attempt
+        // so it makes sense for them to be able to leave the current unit by clicking arrow buttons
+        notify('navigation', {state: 'unlock'});
+
         cleanAll();
         showReviewStep();
         showAttempts();
@@ -343,6 +353,11 @@ function MentoringWithStepsBlock(runtime, element) {
     }
 
     function handleTryAgain(result) {
+        // Tell supporting runtimes to disable navigation between units;
+        // this keeps users from accidentally clicking arrow buttons
+        // and interrupting their experience with the current unit
+        notify('navigation', {state: 'lock'});
+
         activeStep = result.active_step;
         clearSelections();
         updateDisplay();
@@ -364,6 +379,13 @@ function MentoringWithStepsBlock(runtime, element) {
         submitXHR = $.post(handlerUrl, JSON.stringify({})).success(handleTryAgain);
     }
 
+    function notify(name, data){
+        // Notification interface does not exist in the workbench.
+        if (runtime.notify) {
+            runtime.notify(name, data);
+        }
+    }
+
     function initClickHandlers() {
         $(document).on("click", function(event, ui) {
             var target = $(event.target);
@@ -382,6 +404,11 @@ function MentoringWithStepsBlock(runtime, element) {
     }
 
     function initXBlockView() {
+        // Tell supporting runtimes to disable navigation between units;
+        // this keeps users from accidentally clicking arrow buttons
+        // and interrupting their experience with the current unit
+        notify('navigation', {state: 'lock'});
+
         // Hide steps until we're ready
         hideAllSteps();