Add findFirst utility method

[x7airworker]

Is your feature request related to a problem? Please describe.
When you want to find a value just by the key, but don't care about the structure, you most likely write a recursive method to do that for you. So I think it would be good to include this utility method into the project.

Describe the solution you'd like
Basically a recursive method for both AbstractObject and AbstractArray.
AbstractElement findFirst(String key)
The method should be on AbstractArray as well, because an AbstractArray could contain objects which contain the key I want to search for.

[JanHolger]

This could be implemented as an extension to the query method, maybe by adding a wildcard placeholder to it