Settings parent child hierarchy

This implements settings hierarchy for editor and view as discussed [here](https://github.com/limetext/lime/issues/197). closes #197
Doesn't need a change in this PR, but I'd just like to comment that #293 should get rid of all these variables. I think most use cases couldn't care less from *where* a package is loaded or how many different paths there are. It'd be nice to have a `type packagePaths []string` or something that maintains the correct priority ordering.