gui: Show Javascript error indicator on dev builds, remove logging of missing translations

gui/default/syncthing/development/logbar.html

@@ -0,0 +1,13 @@
+<div class="dev-top-bar" id="dev-top-bar">
+    <link href="assets/css/dev.css" rel="stylesheet">
+    <div class="row">
+        <div class="col-xs-4"><b>DEV</b></div>
+        <div id="log" class="col-xs-8">
+            <span>
+                JS:
+                <span class="dev-error fa fa-exclamation-triangle"> errors <span id="log_error">0</span></span>
+                <span class="dev-warn fa fa-frown-o"> warn <span id="log_warn">0</span></span>
+            </span>
+        </div>
+    </div>
+</div>

gui/default/syncthing/development/logbar.js

@@ -0,0 +1,39 @@
+'use strict';
+
+function intercept(method, handler) {
+    var console = window.console;
+    var original = console[method];
+    console[method] = function () {
+        handler(method);
+        // do sneaky stuff
+        if (original.apply) {
+            // Do this for normal browsers
+            original.apply(console, arguments);
+        } else {
+            // Do this for IE
+            var message = Array.prototype.slice.apply(arguments).join(' ');
+            original(message);
+        }
+    };
+}
+
+function handleConsoleCall(type) {
+    var element = document.querySelector('#log_' + type);
+    if (element) {
+        if (!element.classList.contains("hasCount")) {
+            element.classList.add("hasCount");
+        }
+
+        var devTopBar = document.querySelector('#dev-top-bar');
+        devTopBar.style.display = 'block';
+
+        element.innerHTML = parseInt(element.innerHTML) + 1;
+    }
+}
+
+if (window.console) {
+    var methods = ['error', 'warn'];
+    for (var i = 0; i < methods.length; i++) {
+        intercept(methods[i], handleConsoleCall);
+    }
+}