ColumnNameAsKeysRowConverter should be able to traverse nested columns

In some modules we have rows/documents that can have nested objects. For instance in the JSON module. Often these modules will use the ColumnNameAsKeysRowConverter class to extract values from it's row/document objects into MetaModel's rows.

It would be a big improvement if we allow the user to specify column names with a syntax that allows them to denormalize their data and extract information even from nested objects. For instance if you have this document:

{
"name":

{ "first":"Joe", "last":"Sixpack" }

,
"gender":"MALE",
"verified":false,
"userImage":"Rm9vYmFyIQ=="
}

Then a column with the name "name.first" should resolve "Joe" from this particular document. I believe we have similar functionality in some of the NoSQL modules, so consider how we can best reuse it.