Fix crash in observing list whenever catalog configuration was changed.

a.k.a. the "Wishlist-Killer" bug.

A very frustrating crash would ensue whenever the catalog
configuration options were changed (eg: adding a new custom catalog)
and an object was added to the observing wishlist. Before a recent
commit, the wishlist would be truncated causing much frustration to
the user.

The crash occurred because the SkyObjects are de-allocated and
re-allocated by SkyMapComposite::reloadDeepSky() every time the
catalog configuration objects have changed. Since the ObservingList
maintained a QList<SkyObject *> pointers to these SkyObjects, we were
often querying dangling pointers, leading to crashes. So addition of
the object to the wishlist, although did trigger the bug, was not the
root cause.

This change fixes the bug (hopefully without inducing any
others!). The changes are:

1. Create a clone of the SkyObject in ObservingList

   This makes add / remove more complicated as they look-up the given
   object by name, but solves the crash because we have a local copy
   of the SkyObject even if the CatalogComponent's copy is deleted.

2. Use QSharedPointer<SkyObject> instead of SkyObject *

   This makes sure that we don't re-create the same object for session
   plan / wish list. Besides, it is much more cleaner, and takes care
   of deleting itself etc.

Extensive testing is appreciated.

And once again, happy 20th Birthday KDE!

BUG: 345348
CCMAIL: kstars-devel@kde.org