Prompt users to migrate base64 images to mediatags in the pad app

www/common/common-util.js

@@ -154,6 +154,22 @@ define([], function () {
         xhr.send(null);
     };
 
+    Util.dataURIToBlob = function (dataURI) {
+        var byteString = atob(dataURI.split(',')[1]);
+        var mimeString = dataURI.split(',')[0].split(':')[1].split(';')[0];
+
+        // write the bytes of the string to an ArrayBuffer
+        var ab = new ArrayBuffer(byteString.length);
+        var ia = new Uint8Array(ab);
+        for (var i = 0; i < byteString.length; i++) {
+            ia[i] = byteString.charCodeAt(i);
+        }
+
+        // write the ArrayBuffer to a blob, and you're done
+        var bb = new Blob([ab], {type: mimeString});
+        return bb;
+    };
+
     Util.throttle = function (f, ms) {
         var to;
         var g = function () {