Bug 1859 - Macros on files - Save Project causes overwrites. thus loses data

AudacityProject::Save() is now batch mode sensitive, and if in batch mode (and not overwriting) will save without prompting.
The loop for applying macros to multiple files now also clears down the project, using the new function ResetProjectToEmpty().

src/UndoManager.cpp

@@ -198,6 +198,8 @@ void UndoManager::RemoveStates(int num)
 void UndoManager::ClearStates()
 {
    RemoveStates(stack.size());
+   current = -1;
+   saved = -1;
 }
 
 unsigned int UndoManager::GetNumStates()