UI: Add option to save projectors

This adds an option to the general settings to save the opened
projectors on exit.

(Note: Fixed conflicts -Jim)

Closes jp9000/obs-studio#743

UI/window-basic-main-scene-collections.cpp

@@ -222,6 +222,9 @@ void OBSBasic::RefreshSceneCollections()
 	EnumSceneCollections(addCollection);
 
 	ui->actionRemoveSceneCollection->setEnabled(count > 1);
+
+	OBSBasic *main = reinterpret_cast<OBSBasic*>(App()->GetMainWindow());
+	main->OpenSavedProjectors();
 }
 
 void OBSBasic::on_actionNewSceneCollection_triggered()