[fearure request] custom default name for scanned docs

[Mattia]

I'd like to have an option in the preference dialog which allow user to define a custom default
name, a custom default naming scheme, in order to get a more reliable saved documents.
and also a custom default folder and default extension, file format, used.

yes, in similar way of sane....

e.g. NAME -> scanned-%nnn.png, will produce these files: scanned-001.png, scanned-002.png, and so on
        NAME -> scanned-%date.jpg, will produce these files: scanned-31-05-2016.jpg, scanned-01-06-2016.jpg, and so on
        NAME -> %nn-scanned-%date.png, will produce these files: 001-scanned-31-05-2016.png, 002-scanned-01-06-2016.png, and so on