Boot activiti

Hi, 

Now that Spring Boot is GA, I want to include a Boot auto-configuration integration. With this, someone needs only link to the Activiti Spring Boot module (which this PR contributes) and - assuming they have a valid `javax.sql.DataSource` defined in the context and they've deployed process definitions in the `src/main/resources/process` directory - the user need only inject a pointer to the fully configured `ProcessEngine` instance. Assuming process definitions in `src/main/resources/processes/`, this is a valid Spring Boot application with a working `ProcessEngine`. 

```
@Configuration
@ComponentScan 
@EnableAutoConfiguration 
public class Application {
    public static void main(String [] args ){
        SpringApplication.run (  Application.class, args ) ;
    }
} // Sets up Spring Boot. No web.xml, persistence.xml, beans.xml, etc.

@Component 
class CartService {

  private final ProcessEngine processEngine ;

  @Autowired 
   CartService( ProcessEngine pe) {  
     this.processEngine = pe ;
   }

   public void startFulfillment( long customerId ) { 
       // use processEngine 
   }
   // ... 
 }
```

Done!