List jobs within a workflow

It'd be great to be able to to list the jobs within a workflow, ie:

```bash
$> sem get workflows <id> --jobs
ID       NAME            AGE   STATE     RESULT
<id>   unit-test          22s    DONE     PASSED
<id>   integration-test         59s    DONE     PASSED
<id>    lint                   22s    DONE     PASSED
```