Set default extensions for most save files

In most of these cases, the open file dialog won't even display a file
without the proper extension, so this helps ensure the user doesn't
accidentally misplace their files. The one exception is *.rdc, which
could be found without the extension, but could not be opened.

qrenderdoc/Windows/PythonShell.cpp

@@ -511,7 +511,7 @@ void PythonShell::on_openScript_clicked()
 void PythonShell::on_saveScript_clicked()
 {
   QString filename = RDDialog::getSaveFileName(this, tr("Save Python Script"), QString(),
-                                               tr("Python scripts (*.py)"));
+                                               tr("Python scripts (*.py)"), lit("py"));
 
   if(!filename.isEmpty())
   {