Fix scaling issues

[cwisniew]

Identify the Bug or Feature request

resolves #3652

Description of the Change

It fixes a problem where some images were scaled as high quality regardless of preference setting. Add text to the Low option for scaling quality, indicating that it is the setting for pixel art based games. Also, changed the default from High to Medium (this will only be picked up when upgrading to 1.12.1 from 1.11.5 or earlier if upgrading from 1.12.0 to 1.12.1, the value will have already defaulted).

Possible Drawbacks

Hopefully none.

Documentation Notes

It fixes a problem where some images were being scaled as high quality regardless of preference setting. Add text to the Low option for scaling quality, indicating that it is the setting for pixel art based games. Also, changed the default from High to Medium (this will only be picked up when upgrading to 1.12.1 from 1.11.5 or earlier if upgrading from 1.12.0 to 1.12.1, the value will have already defaulted).

Release Notes

• Medium is now the default scaling quality when upgrading from 1.11 or earlier.
• Image scaling on all layers should now respect preferences choice.
• Use Low scaling quality for pixel art games.

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This change is 

[Phergus]

Reviewed 5 of 5 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @cwisniew)