JsonNode, ArrayNode and ObjectNode extensions

[sokomishalov]

Implements #492

[cowtowncoder]

This seems like potentially useful (if I understand the intent) additions.
I think it'd be useful to have couple of more things included:

1. Issue with actual description of why and what (could just add Description to PR too)
2. Basic unit test coverage
3. A small bit of documentation on either README.md of Kotlin module, or under Wiki -- explaining use of these additional operations.

[sokomishalov]

@cowtowncoder sure, done

[cowtowncoder]

Thanks! I'll let module owners review this otherwise. This may still make it in 2.13.0 if they approve (I pushed last rc, 2.13.0-rc2 last night, but 2.13.0 won't be out until next weekend or weekend after that).

[dinomite]

@sokomishalov Have you signed the CLA? If not, would you fill it out and email a scan/photo of the result to info at fasterxml dot com?

https://github.com/FasterXML/jackson/blob/master/contributor-agreement.pdf

[sokomishalov]

@dinomite I've signed and sent the document to the mailbox, also made changes due to your suggestions, please have a look again

[cowtowncoder]

CLA received just like @sokomishalov said.

[cowtowncoder]

I wonder if it'd make sense to add one more cla-related labels (cla-needed, cla-available ... or something)?
One challenge may be that only admins can add/remove labels.