Fix to expand refs before creating root editor

[ianmetcalf]

I ran into an issue when using $ref in the root schema, where the schema in the file referenced doesn't get expanded. Here is an example that reproduces this:

vareditor=newJSONEditor(element,{ajax: true,schema: {$ref: '/schema/a.json',}});

{"id": "/schema/a.json", "oneOf": [{"$ref": "/schema/b.json" },{"$ref": "/schema/c.json" } ] }

I fixed this be expanding the refs in the root schema before instantiating the root editor.

Also, I had to use node v0.10 in order to run grunt. You may want to make a note of that in the README or upgrade the grunt jshint package to support newer versions of node.