Allow the app to use the same directory for opening and saving.

[BeastOfBodmin]

I have been unable to test this, since I don't know how to repackage the app. But I simply removed the "initialdir=self.output_dir" argument from the filedialog.ask* calls.

According to stackoverload, this means the app will remember the last used directory between runs (maybe), or within a given session (I hope!)