Refactor Customer fixture

[walterdolce]

• Added service container.
• Delegating websites related date responsibility to the Website helper class.

[jamescowie]

Good work,

[alistairstead]

I don't like the service container being injected. This is a a close coupling to the container this is not the dependency inversion principle. There is now significant and inappropriate intimacy between the fixture class and the container. These collaborators should be injected at the constructor based on appropriate type hinted parameters. Please see my upcoming PR that includes and expanded service container definition that should form an example of the required changes.