Add the possibility of listing the children of a document in a livetable

I did this for one of the client projects.

The solution is to use this piece of code in XWiki/LiveTableResults:

#if("$!request.parent" != '')
#set($extra = "${extra} and doc.parent = '${request.parent}'")
#end

and then pass "&parent=spaceName.docName" to the extraParams parameter of the livetable $options hash