Improve log messages to make them more consistent

[clebert]

• integrator.js:6 The feature app module for the url "feature-app.umd.js" has been successfully loaded.
• integrator.js:6 All required feature services have been successfully bound to the consumer "test:hello-world".
• integrator.js:6 The feature app scope for the ID "test:hello-world" and its specifier undefined has been successfully created.

      `The feature app for the src ${JSON.stringify(
        src
      )} and the ID specifier ${JSON.stringify(
        idSpecifier
      )} could not be loaded.`,
        error
      );