Remove extension loading error log when not in dev mode.

vispa/static/js/extensions.js

@@ -42,8 +42,11 @@ define(["jquery", "emitter", "vispa/module", "vispa/ui"], function($, Emitter, M
       this.extensionsLoading++;
       require(["extensions/"+name+"/static/js/extension"],
         this.registerExtension.bind(this),
-        function (err){
-          self.logger.error("extension '%s' failed to load due to: %s", err.requireModules[0].split("/")[1], err.requireType);
+        function(err) {
+          if (vispa.args.global.devMode) {
+            self.logger.error("extension '%s' failed to load due to: %s",
+              err.requireModules[0].split("/")[1], err.requireType);
+          }
           self._checkExtensionsLoaded();
       });