Makes scaling optional to keep original image dimension

[repraze]

Open for comments on overall solution.

• Adds a scaling toggle to skip the fill/fit/stretch mode.
• Renamed scaling to scalingMode and reused scaling to contain Boolean value.
• Makes scaling enabled by default. Could potentially change that. (Still needs proper testing on a fresh start with no data)

This solution allows the OS to do the sizing and enables proper parallax on pixel OS.

Disabled	Enabled

Considerations

• An alternative implementation would be to add another ScalingConstants with None or Default to let the OS take over the scaling. The radio input seems crowded for a fourth option though. I thought the additional checkbox was in line with other toggleable settings.
• The new Resize string is not properly translated. I wasn't sure about the process here.
• Not sure if renaming scaling to scalingMode might have non-backward compatible issue with reading the saved settings. If so, we could keep the string binding the same for backward compatibility.

relates to https://github.com/Anthonyy232/Paperize/issues/92