Add support for bulk-updating multi-line translations

http://manage.dimagi.com/default.asp?146611

@amsagoff this seems like a new feature since the old parser definitely did not support multi-line translations with un-escaped newline characters. Does this seem like a win to you?
Previously the header row was ignored and the form/lang was derived from the XForm's list of languages and a hard-coded list (see `exportCols` above). This seemed fragile since rearranging columns in the Excel file would reassign translations in a surprising way. The header row is now used to determine itext form/lang info. A side effect of this new implementation is that translation values with languages not in this XForm's list of languages will be ignored (previously they would have been stuffed into the wrong language or into a different itext form, which was just plain wrong).