add undo/redo shortcut and idea selection-indicator to LabyrinthJS

While linking ideas, no selection-indicator of selected idea was visible thereby creating confusion.
Added a selection-indicator to the currently selected idea and auto-deselect after making a link.

Signed-off-by: Aayush Raj <[email protected]>

activities/LabyrinthJS.activity/js/activity.js

@@ -362,11 +362,18 @@ define(["sugar-web/activity/activity", "l10n", "sugar-web/datastore", "sugar-web
 				if (lastSelected == this) lastSelected = null;
 				return;
 			} else if (currentMode == 1) {
+				if (isSelectedNode(this)) {
+					unselectNode(this);
+					lastSelected = null;
+				}
+				else { selectNode(this); }
 				if (lastSelected != null && lastSelected != this) {
 					createEdge(lastSelected, this);
+					unselectNode(this);
+					lastSelected = null;
 					pushState();
 				}
-				lastSelected = this;
+				if (isSelectedNode(this)) lastSelected = this;
 				return;
 			} else {
 				if (isSelectedNode(this)) {
@@ -639,6 +646,14 @@ define(["sugar-web/activity/activity", "l10n", "sugar-web/datastore", "sugar-web
 		undoButton.addEventListener('click', function () { undoState(); }, true);
 		var redoButton = document.getElementById("redo-button");
 		redoButton.addEventListener('click', function () { redoState(); }, true);
+		document.addEventListener('keydown', function (event) {
+			if (event.ctrlKey && event.key === 'z' || event.key === 'Z') {
+				undoState();
+			}
+			if (event.ctrlKey && (event.key === 'y' || event.key === 'Y')) {
+				redoState();
+			}
+		});
 
 		var reinitState = function() {
 			stateHistory = [];