$RestxSession special header, more samples in AppModule generated file (app.name, security) & test harness for restx-core-shell

Taking into account :
- The new `app.name` component (using the `restx shell`'s `appName` property)
- Changing ordering of components, putting `SignatureKey` first, in order to follow documentation ordering on [Generated app explained's AppModule section](http://restx.io/docs/generated-app-explained.html)

During implementation, some new features appeared :
- Implementing a `$RestxSession` special header in `restx specs` files, allowing to define a restx session content (with proper cookie name, given available `RestxCookieDescriptor` component) and sign it with current `SignatureKey` component
- Improved HelloResource sample by providing a basic security implementation sample and using the `@RolesAllowed` annotation
- Provided a test harness in `restx-core-shell` allowing to validate that `app new` shell command generates a new app and this app has green tests