Default value for radio button of image format and Submap

When exporting a submap from graphics, the value "Core PD Map" for "Submap", and the value "PNG Image" for "Image format" should be selected by default.

changed milestone to %18.0.0~beta.5

added Feature label

created branch 295-default-value-for-radio-button-of-image-format-and-submap to address this issue

mentioned in merge request !250 (merged)

closed

Tested, works.