Fixed default image blink on load

.gitignore

@@ -36,6 +36,7 @@ htmlcov/
 .tox/
 .coverage
 .cache
+.noseids
 nosetests.xml
 coverage.xml
 
@@ -53,3 +54,7 @@ docs/_build/
 target/
 
 workbench.db
+
+# IDEs
+.idea
+.idea/*

drag_and_drop_v2/public/css/drag_and_drop.css

@@ -86,6 +86,7 @@
 }
 
 .xblock--drag-and-drop .target-img {
+    display: none;
     background: url('../img/triangle.png') no-repeat;
     width: 100%;
     height: 100%;

drag_and_drop_v2/public/js/drag_and_drop.js

@@ -74,6 +74,9 @@ function DragAndDropBlock(runtime, element) {
                 if (_fn.data.targetImg)
                     _fn.$target.css('background', 'url(' + _fn.data.targetImg + ') no-repeat');
 
+                // Display target image
+                _fn.$target.show();
+
                 // Display the zone names if required
                 if (_fn.data.displayLabels) {
                     $('p', _fn.$zones).css('visibility', 'visible');
@@ -287,7 +290,7 @@ function DragAndDropBlock(runtime, element) {
                             content: _fn.$popup.find(".popup-content").text(),
                             manually: false
                         });
-                    };
+                    }
                     publish_event({
                         event_type: "xblock.drag-and-drop-v2.feedback.opened",
                         content: str