Feature/json serialization

[arielshulman]

Hey,
As discussed in #88 issue, I've made a quick fix which enable JSON serialization.
Some quick notes -

1. I've created new initialJson and onJsonChange props to the component.
2. I've added a new onImportError which I think should unify import errors and replace onImportXmlError.
3. I didn't treat odd situations when someone used initialJson and initialXml simultaneously .
4. The onJsonChange is executed based on the current mechanism which depends on xml changes.

What do you think?

[nbudin]

Great, thanks for doing this @arielshulman! This all looks good to me, and I agree with consolidating the import error callbacks. Assuming the CI checks pass, I'll merge and release this.