supporting applicationConfigFiles definition in a setting other than master

specifically supporting runtime:common or runtime:server, e.g.: 

```
[
    {
        "settings": [ "runtime:common" ],
        "applicationConfigFiles": [
            "another/application.json",
            "master-setting.json"
        ]
    },
    {
        "settings": [ "master" ],
        "testKey1": "testVal1",
        "testKey2": "testVal2",
        "testKey3": "testVal3"
    }
]
```

So, you can get a master setting that is shared between apps, and include it as part of the root application.json