Add redo button

public/index.html

@@ -54,6 +54,9 @@
 			<button id="whiteboardUndoBtn" title="Undo your last step" type="button" class="whiteboardBtn">
 				<i class="fa fa-undo"></i>
 			</button>
+			<button id="whiteboardRedoBtn" title="Redo your last undo" type="button" class="whiteboardBtn">
+				<i class="fa fa-redo"></i>
+			</button>
 		</div>
 
 		<div class="btn-group">

public/js/main.js

@@ -256,6 +256,11 @@ $(document).ready(function () {
         whiteboard.undoWhiteboardClick();
     });
 
+    // redo button
+    $("#whiteboardRedoBtn").click(function () {
+        whiteboard.redoWhiteboardClick();
+    });
+
     // switch tool
     $(".whiteboardTool").click(function () {
         $(".whiteboardTool").removeClass("active");