fix for annoying and false AutoMoc warning

the line with:
LIST(APPEND CMAKE_AUTOMOC_MACRO_NAMES "KWAVE_PLUGIN")

now has to be set *after* FIND_PACKAGE(Qt5 Core ...), otherwise the list would be overwritten and produce many annoying build warnings like these:

AutoMoc warning
---------------
"SRC:/plugins/<plugin>/<file>.cpp"
includes the moc file "<file>.moc", but does not contain a Q_OBJECT, Q_GADGET, Q_NAMESPACE, Q_NAMESPACE_EXPORT, K_PLUGIN_FACTORY, K_PLUGIN_FACTORY_WITH_JSON, K_PLUGIN_CLASS_WITH_JSON, K_PLUGIN_FACTORY, K_PLUGIN_FACTORY_WITH_JSON, K_PLUGIN_CLASS_WITH_JSON, K_PLUGIN_FACTORY, K_PLUGIN_FACTORY_WITH_JSON, K_PLUGIN_CLASS_WITH_JSON, K_PLUGIN_FACTORY, K_PLUGIN_FACTORY_WITH_JSON, K_PLUGIN_CLASS_WITH_JSON, K_PLUGIN_FACTORY, K_PLUGIN_FACTORY_WITH_JSON, K_PLUGIN_CLASS_WITH_JSON, K_PLUGIN_FACTORY, K_PLUGIN_FACTORY_WITH_JSON, K_PLUGIN_CLASS_WITH_JSON, K_PLUGIN_FACTORY, K_PLUGIN_FACTORY_WITH_JSON, K_PLUGIN_CLASS_WITH_JSON, K_PLUGIN_FACTORY, K_PLUGIN_FACTORY_WITH_JSON or K_PLUGIN_CLASS_WITH_JSON macro.