BUG: 285778 - View or edit files doesn't work

If no KParts/ReadWritePart is available, notify the user and sugest installing Kate.
Viewer not working has been fixed by
http://quickgit.kde.org/index.php?p=krusader.git&a=commit&h=31899e9a281a1da906deb830eafa67e07e0c2282