Add migration to new core data model that doesn’t use image thumbnails.
Remove OEDBImageThumbnail class. Delete thumbnail image files on migration.
Rewrite OEDBImage.
OEDBGame does not generate thumbnails anymore.
Set default image format to jpg with compression factor of 0.9.
Convert images to jpg after migration.
Fix some bugs introduced in previous commits.
Add support for custom game view background color (#1232).
Allow setting game view background color from ‘Secrets’ pane (Fix #1232).
Remove last traces of image thumbnails.