Port the plugin system to the standard KDE factory and loader, getting rid of the custom system okular had so far.
This requires a generator to have a
  MyGenerator(QObject *parent, const QVariantList &args)
constructor in order to be successfully loaded.
The OKULAR_EXPORT_PLUGIN macro was adapted, and the generators to provide it the about data; the protected Generator::setAboutData() is no more needed.

Remove the 'lib' prefix from plugins, unneeded now.

CCMAIL: okular-devel@kde.org

svn path=/trunk/KDE/kdegraphics/okular/; revision=744169