Add option to not move but copy the selected AppImage

[darealshinji]

Let's say I have a copy of an AppImage in a directory stored as a backup, integrating it with the AppImageLauncher will delete it from my backup directory. Putting an option to the settings to disable this behaviour on the user's wish would be great.

[TheAssassin]

I have been thinking about a new UI that provides more options. I don't think we should bloat the current dialog with more checkboxes or anything.

Note: I assume this is a per-AppImage decision to make.