Add support for importing in the data space of an App Within Minutes

Starting with nested spaces (version 7.3 + or something like this), the App Within minutes puts data, by default in the .Data subspace of the application space (see XWIKI-12741 ).
The Batch Importer application default wizard is made to import data in an AWM, but does not support this .Data subspace (it would import them in the application toplevel space).
We need to add support for this Data space, preferably with a proper fallback on the previous format of application, to still support all types of applications created with AWM.