message: QTAIM needed Qt5 concurrent on the extension
  The scene plugin does nothing in parallel, this one was perhaps a little
  confusing as two plugins are built. Moved the concurrent to the correct
  place, and used the more modern style.
diff: @@ -18,6 +18,10 @@ avogadro_plugin(QTAIMExtension
  "${qtaimextension_SRCS}"
  )
  +target_link_libraries(QTAIMExtension
  + LINK_PRIVATE
  + Qt5::Concurrent)
  +
  # The settings widget is not built -- its settings weren't actually used by the
  # engine in Avogadro 1. The sources are kept for later if we decide to use it.
  avogadro_plugin(QTAIMScenePlugin
  @@ -29,4 +33,5 @@ avogadro_plugin(QTAIMScenePlugin
  )
  target_link_libraries(QTAIMScenePlugin
  - LINK_PRIVATE AvogadroRendering ${Qt5Concurrent_LIBRARIES})
  + LINK_PRIVATE
  + AvogadroRendering)
  