gui: cleanup some string constants for translations * file-editor.h: deleted constants for file filters and name for new files * file-editor.cc (request_open_file): translate file filter in open dialog * file-editor.cc (request_new_file): create new edit tab with empty title because the title is updated later * file-editor-tab.cc (update_window_title): translate unnamed title * file-editor-tab.cc (save_file_as): translate file filter, shorter warning message when new file name is the same as the current one

--- a/libgui/src/m-editor/file-editor.h
+++ b/libgui/src/m-editor/file-editor.h
@@ -33,8 +33,6 @@
 #include "file-editor-interface.h"
 #include "file-editor-tab.h"
 
-const char UNNAMED_FILE[]     = "<unnamed>";
-const char SAVE_FILE_FILTER[] = "Octave Files (*.m);;All Files (*.*)";
 enum editor_markers
   {
     bookmark,