List targets and processes

`ggg list` will now list targets and processes if a target has multiple processes. For example, if your ggg file looks like this:

```javascript
module.exports = {
  start: {
    foo: 'bar',
    baz: 'beans'
  },
  targets: {
     dev: 'dev@example.com'
  }
}
```

Then the output of `ggg list` should look like this:

```bash
dev:foo
dev:baz
```