Allow to authenticate and launch an application offline

[claustres]

Authentication requires a call to the authentication service that will not be available when offline.

Depending on the application some services should also be available to launch it, we should provide a way to cache selected Feathers services and associated data using https://github.com/feathersjs-offline/localforage.

• cached authentication information
• function to create an offline service
• function to make a snapshot of data coming from an online service into the corresponding offline service

Prototype started on branch https://github.com/kalisio/kdk/tree/offline.