Allow passing configurations to workers via package.json

This allows you to send configuration over to the workers via your
hoodie applications package.json like:

```json
{
  "dependencies": {
    "hoodie-app": "git://github.com/nnarhinen/hoodie-app.git#feature/workerconfigurations",
    "hoodie-worker-users": "git://github.com/hoodiehq/worker-users.git",
    "hoodie-worker-my-great-worker": "git://..."
  },
  "workerConfigurations": {
    "my-great-worker": {
      "foo": "bar"
    }
  }
}
```