Create service_example

Problem/Motivation

Drupal 8 introduces the concept of a service discovery container and services.

We need an example of how to create a service.

Proposed resolution

Create a service_example module.

Some requirements:

1. Shows how to create a service.
2. Shows how to take advantage of inversion of control and container injection.
3. Shows how and when to use \Drupal.

Also checklist stuff: #2209627: [meta] Module Checklist for Examples →

Remaining tasks

User interface changes

API changes

Data model changes