Settings parent child hierarchy

This implements settings hierarchy for editor and view as discussed [here](https://github.com/limetext/lime/issues/197). closes #197
The json parser is [here](https://github.com/limetext/lime/blob/master/backend/loaders/json.go) in `github.com/limetext/lime/backend/loaders` package and IIRC it supports trailing commas.