feat(log): support optional log level param to developmentLogging().

So we can do aurelia.use.developmentLogging(environment.debug ? 'debug' : 'warn'); to still see error/warn in production app.

src/framework-configuration.js

@@ -350,14 +350,20 @@ export class FrameworkConfiguration {
 
   /**
    * Plugs in the ConsoleAppender and sets the log level to debug.
+   * @param level The log level (none/error/warn/info/debug), default to 'debug'.
    * @return {FrameworkConfiguration} Returns the current FrameworkConfiguration instance.
   */
-  developmentLogging(): FrameworkConfiguration {
+  developmentLogging(level?: String): FrameworkConfiguration {
+    let logLevel = level ? TheLogManager.logLevel[level] : undefined
+    if (logLevel === undefined) {
+      logLevel = TheLogManager.logLevel.debug;
+    }
+
     this.preTask(() => {
       return this.aurelia.loader.normalize('aurelia-logging-console', this.bootstrapperName).then(name => {
         return this.aurelia.loader.loadModule(name).then(m => {
           TheLogManager.addAppender(new m.ConsoleAppender());
-          TheLogManager.setLevel(TheLogManager.logLevel.debug);
+          TheLogManager.setLevel(logLevel);
         });
       });
     });