Better handling of data flow

[MertenD]

Description

Currently all the nodes have a list of values as a output. That is not necessary optimal for many nodes. For example when the extractor node is extracting multiple elements for each of the input elements is might be useful to group the extracted elements together.

Currently it looks like:

Input: [1, 2]
Output: [1.1, 1.2, 2.1]

I need something like this, where the context from where it is coming from remains:

Input: [1,2]
Output: [[1.1, 1.2], [2.1]]

Both Outputs have their own unique use cases. There should be a system that supports both. Maybe it could be useful to do the second approach as a default and to offer an option to flatten the output. Either by creating a new node for it or by putting it as a default option in the options of a node.