Application engine

* Adding a workspace configuration class, matching a JSON file

  The workspace configuration contains a property 'applications',
  an array of ApplicationConfiguration object.

  An application configuration is a specific URL binding, and
  navigation information (localized message and icon).

* Adding a Message class to store a localizable message.

* Adding an hello world application to demonstrate how an user
  can write a new application.

* Navigation shows these customs applications.

* Entry point calls relevant application controller.