export similar to result view as concerns content and format

For example, when a table is exported, it should keep the same columns, in the same order, and the same format for numbers in the cells.

Md: to be linked to the generic export mecanism to implement in TXM 0.8.2 or later versions.

(from redmine: issue id 198, created on 2013/07/04 by Benedicte Pincemin)