Improving the DSS image retrieval feature (as accessed from
KSPopupMenu) smarter.

For deep-sky objects, it now uses an image height and width computed
to fit the deep-sky object with some additional padding (currently
hardcoded). Absurd values are replaced by a default size (which is
currently hard-coded to 15 arcminutes).

It uses the hardcoded default size value for all other objects.

FEATURE