Fixing a lot of issues caused by translated planet names.

These are temporary "ugly" fixes, before the KDE 4.2 release that we might want to revert and re-design later.

The trouble is that in the case of Sun, Earth and Moon, the name() method returns the English name whereas on other planets, it returns the translated name (while that's not the way it should be, according to the documentation in skyobject.h).
A quick fix for this is to make sure that we always use the translated name to find the planet.

There will still be (minor) issues with languages that have a translation for Pluto.