update release notes for v1.48.1

ReleaseNotes

 Release notes
 TSG-QC   jacques.grelet@ird.fr
 
+v1.48.1 (2018-05-29)
+- correct a bug if user select a file with *.* extension
+- the last TSG file type opened stay as default  
+
+v1.48.0 (2018-05-25)
+- Move mean and standard dev in same dialog box
+- implement Undo/Redo for QC 
+ 
 v1.47.0 (2018-03-28)
 - The radio button QC now follows the last selected in the
   contextual menu.