Preview resizing process

[esimov]

Is your feature request related to a problem? Please describe.

The progress indicator bundled into the CLI utility does its job in the sense that at least offer some indication about the work happening in the background, however it does not present a clear visual indication of the effective process.

Describe the solution you'd like

I'm suggesting including a new flag among the existing ones, which when is getting activated a GUI window will show up where the user could see effectively the resizing progress.

By constantly getting notified about the outcome the user could decide at each phase of the resizing process if the outcome is the desired one or not, in case might shut down the whole resizing process and should start over. With the CLI progress indicator the user might check the final image only after it has been generated.

[esimov]

I opted to use the Gio GUI for showing the resize process in a preview window because it's a modern framework with a lot of adopters which is continuously updated and maintained.