Add support for importing documents in a nested space

There is multiple support that can be added for nested spaces in the batch import, but this issue is about the following case:

The lines from the excel / csv are to be added, as terminal pages (current behaviour), in a space which is nested (set as the default space in the batch import configuration).
The simplest example is the new format of the AWM, which puts data in <AWMSpace>.Data . The batch import needs to be able to do the same.

Please note that ideally this change should not bump the minimum supported version for the batch importer, we should figure out a way to handle this that is compatible with both nested spaces and non-nested spaces.