added ability to configure the package name that is scanned for jobs to run

Dropwizard-jobs wasn't picking up my jobs when integrating to dw0.6.2, Reflections was complaining on scan() with "given scan urls are empty. set urls in the configuration". This fix allows explicit configuration of the package names when wiring the JobsBundle into the bootstrap 

```java
    @Override
      public void initialize(Bootstrap<DelaSearchConfiguration> bootstrap) {
      bootstrap.setName("myService");
      bootstrap.addBundle(new JobsBundle("com.package.to.scan"));
    }
```