Add task metadata

Metadata is supported in the config file on a per-task basis. It is to be put
in the 'meta' key's value json.

Currently 'title' and 'description' keys are supported. See the example below.

```
[
    {
        "meta" : {
            "title" : "This is the title",
            "description" : "This is a longer description, not shown with -Q"
        }
    }
]
```