Export subsets of data through editor GUI and task overview

add the possiblity to export a task in the editor to the "Aufgaben"-Button
no combination of different export options (like by date and filters)

For sdlxliff a subsets makes no sense since always the whole file is needed in Trados Studio. Therefore here the whole file is always exported but only the segments of the selected subsets will be replaced with the edited content – for the rest the original translation is kept.