Let other modules create "internal" presets

Hi,

this feature came to my mind while working with Image Browser. IB creates a preset called "ib_thumbnail" for creating the thumbnails in its insert dialog. This approach causes a problem, if the site maintainer doesn't want his/her users to be able to insert 100x100 images into their content.

A solution to this would be to allow modules to mark their presets as "internal". These presets would still be shown at admin/build/imagecache (though not editable), but not to the user (e.g. in IB).

Keep up the great work!

Best regards,
Lars