GUI: data dialog: convert Line Feeds if escaping on input, escape on output

and set Escaped flag; fix tooltip that they're converted to spaces;
  sequence dialog: re-organize to put Create Sequence stuff only in groupbox
  and put Import -> From File and Clear at bottom, similar to data dialog;
  mainwindow: use new Escaped flag from data dialog and set checkbox and
  statusbar message accordingly

frontend_qt/cliwindow.cpp

@@ -25,7 +25,6 @@
 
 #include "cliwindow.h"
 #include "barcodeitem.h"
-#include "mainwindow.h"
 
 // Shorthand
 #define QSL QStringLiteral