Updates to SkyPoint to improve positions

Summary:
Many places in Kstars abd EKOS us precession only to change J2000 catalogue
coordinates to the observed position, omitting nutuation and aberration.
Also the conversion from an observed position to a J2000 catalogue
position was implemented incorrectly, aberration and nutauion were not being removed.

This updates SkyPoint to correct these and adds unit tests to check them.
I also found that the SkyPoint aberration and nutation corrections gave
incorrect results and these have been replaced by the libnova corrections
which testing show are better. I am using SOFA to generate test positions.

The changes to SkyPoint have been used to implement coordinate conversions
correctly in KStars and EKOS, by replacing precession conversion with
apparentCoord() and CatalogueCoord() as appropriate.

Test Plan:
Run the test_skypoint test. At present two tests fail by a small amount for
declinations close to 90.

Review the changes. I don't think I've made a change which isn't required but
may have missed some.

Build and test. For example the details dialog should now give a J2000
position that matches the J2000 positionin the image header. Make sure that
you have an up to date version if INDI. I had to update that as well.

Reviewers: mutlaqja, TallFurryMan

Reviewed By: mutlaqja

Subscribers: kde-edu

Tags: KDE Edu

Differential Revision: https://phabricator.kde.org/D29549