Add error message on JS or LESS blocking error

customize.dist/loading.js

@@ -260,6 +260,11 @@ button.primary:hover{
             '<p id="cp-loading-message"></p>',
         '</div>'
     ].join('');
+    window.CryptPad_loadingError = function (err) {
+        document.querySelector('.cp-loading-spinner-container').setAttribute('style', 'display:none;');
+        document.querySelector('#cp-loading-message').setAttribute('style', 'display:block;');
+        document.querySelector('#cp-loading-message').innerText = err;
+    };
     return function () {
         var intr;
         var append = function () {

www/common/LessLoader.js

@@ -167,7 +167,12 @@ define([
             if (css) { return void loadSubmodulesAndInject(css, url, done, stack); }
             console.debug('CACHE MISS ' + url);
             ((/\.less([\?\#].*)?$/.test(url)) ? loadLess : loadCSS)(url, function (err, css) {
-                if (!css) { return void console.error(err); }
+                if (!css) {
+                    if (window.CryptPad_loadingError) {
+                        window.CryptPad_loadingError('LESS: ' + (err && err.message));
+                    }
+                    return void console.error(err);
+                }
                 var output = fixAllURLs(css, url);
                 cachePut(url, output);
                 loadSubmodulesAndInject(output, url, done, stack);

www/common/sframe-boot2.js

@@ -42,6 +42,9 @@ define([
             console.error("Require.js threw a Script Error. This probably means you're missing a dependency for CryptPad.\nIt is recommended that the admin of this server runs `bower install && bower update` to get the latest code, then modify their cache version.\nBest of luck,\nThe CryptPad Developers");
             return void console.log();
         }
+        if (window.CryptPad_loadingError) {
+            window.CryptPad_loadingError(e);
+        }
         throw e;
     };