Showing J2000.0 coordinates in the Details dialog.

TODO:

1. Fix bugs and make sure that we are _actually_ showing J2000.0.

   We _know_ this is not the case really, as per a recent discussion
   on the kstars-devel Mailing List -- some stars have catalog
   coordinates from a different epoch, but we assume they are J2000.0;

   This leads to visible errors in matching DSS overlays, for example
   (which I think I did notice at the Texas Star Party).

2. Improve the Astroinfo article on precession, to which the J2000.0
   RA and Dec labels are hyperlinked. The article on precession
   doesn't talk about epochs.

CCMAIL: kstars-devel@kde.org
FEATURE: 211838