File chooser dialogs are awkward

[sjackso]

Dialog boxes for saving files and screenshots awkwardly say "Open" instead of "Save," because we're using QFileDialog.getExistingDirectory(). A custom directory with custom buttons would be better.

In addition, Mark notes that the default directory presented by the Save Results dialog is weird, (probably) especially when running from app translocation on a freshly downloaded Athena.app.