Configuration: set default image interpolation to anti-aliasing (`5` instead of `0` for nearest)

[PierreRaybaut]

This option would toggle the anti-aliasing interpolation mode for displaying images.

Currently (and after this change as well), the default interpolation mode is "no interpolation" (nearest).

[PierreRaybaut]

Change of plans: the original need may be answered by simply changing the default interpolation value in configuration.
This may also be changed by the user from the settings dialog, through the default visualisation settings ("View" tab).