feat(index.html): reload when resource fails to load

The page will be reloaded if any of the mandatory scripts/resources
fails to load. The reload will be delayed with exponential backoff
starting from 2 seconds. The retry attempt counter is passed as
'rCounter' query attribute.

index.html

@@ -31,6 +31,40 @@
                     document.body.innerHTML
                         = "The application failed to load, missing file: "
                         + fileRef;
+
+                    // The whole complex part below implements page reloads with
+                    // "exponential backoff". The retry attempt is passes as
+                    // "rCounter" query parameter
+                    var href = window.location.href;
+
+                    var retryMatch = href.match(/.+(\?|&)rCounter=(\d+)/);
+                    var retryCountStr = retryMatch ? retryMatch[2] : "0";
+                    var retryCount = Number.parseInt(retryCountStr);
+
+                    if (retryMatch == null) {
+                        var separator = href.indexOf("?") === -1 ? "?" : "&";
+                        var hashIdx = href.indexOf("#");
+
+                        if (hashIdx === -1) {
+                            href += separator + "rCounter=1";
+                        } else {
+                            var hashPart = href.substr(hashIdx);
+
+                            href = href.substr(0, hashIdx)
+                                + separator + "rCounter=1" + hashPart;
+                        }
+                    } else {
+                        var separator = retryMatch[1];
+
+                        href = href.replace(
+                            /(\?|&)rCounter=(\d+)/,
+                            separator + "rCounter=" + (retryCount + 1));
+                    }
+
+                    var delay = Math.pow(2, retryCount) * 2000;
+
+                    window.setTimeout(
+                        function () { window.location.replace(href); }, delay);
                 };
                 window.removeEventListener(
                     'error', loadErrHandler, true /* capture phase */);