[wip] Trade: full scene conversion support in AbstractSceneConverter.

TODO: changelog
TODO: putting the delegation to single-mesh into batch do*() APIs and
  vice versa feels wrong as they're called even if the feature is not
  supported, should be done by the driver instead
TODO: coverage is sad

src/MagnumPlugins/AnySceneConverter/AnySceneConverter.cpp

@@ -98,4 +98,4 @@ bool AnySceneConverter::doConvertToFile(const MeshData& mesh, const Containers::
 }}
 
 CORRADE_PLUGIN_REGISTER(AnySceneConverter, Magnum::Trade::AnySceneConverter,
-    "cz.mosra.magnum.Trade.AbstractSceneConverter/0.1.2")
+    "cz.mosra.magnum.Trade.AbstractSceneConverter/0.2")