Create new unified Overlay transform

This MR creates a new unified Overlay transform targeting to merge MC and data overlay and be MT friendly. It is still in very early stages but SCT and truth overlays can be run with threads > 1. Please ignore commented-out code for now as things will probably still change a lot.

Current transforms should still work and the output should not change.

Event/EventOverlay/EventOverlayJobTransforms/python/overlayTransformUtils.py

-# Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+# Copyright (C) 2002-2019 CERN for the benefit of the ATLAS collaboration
 
 ## @brief Specialist reconstruction and bytestream transforms
 #  @author atlas-comp-jt-dev@cern.ch
@@ -209,6 +209,19 @@ def addOverlay_BSSubstep(executorSet):
                                    substep = 'overlayBS', tryDropAndReload = False, perfMonFile = 'ntuple.pmon.gz',
                                    inData = [('HITS', 'BS_SKIM')], outData = ['RDO', 'RDO_SGNL']))
 
+# New common overlay skeleton
+def addOverlaySubstep(executorSet, inRecoChain = False):
+    executor = athenaExecutor(name = 'Overlay', skeletonFile = 'EventOverlayJobTransforms/skeleton.Overlay_tf.py',
+                              substep = 'overlay', tryDropAndReload = False, perfMonFile = 'ntuple.pmon.gz',
+                              inData = [('HITS', 'RDO_BKG')], outData = ['RDO', 'RDO_SGNL'])
+
+    if inRecoChain:
+        executor.inData = []
+        executor.outData = []
+ 
+    executorSet.add(executor)
+
+
 ### Append Sub-step Methods
 def appendOverlayBSTrigFilterSubstep(trf):
     executor = set()
@@ -229,3 +242,16 @@ def appendOverlay_BSSubstep(trf):
     addOverlay_BSSubstep(executor)
     trf.appendToExecutorSet(executor)
 
+# New common overlay skeleton
+def addOverlayArguments(parser):
+    from SimuJobTransforms.simTrfArgs import addBasicDigiArgs, addForwardDetTrfArgs
+    from EventOverlayJobTransforms.overlayTrfArgs import addOverlayTrfArgs, addOverlayPoolTrfArgs
+    addBasicDigiArgs(parser)
+    addForwardDetTrfArgs(parser)
+    addOverlayTrfArgs(parser)
+    addOverlayPoolTrfArgs(parser)
+
+def appendOverlaySubstep(trf, inRecoChain = False):
+    executor = set()
+    addOverlaySubstep(executor, inRecoChain)
+    trf.appendToExecutorSet(executor)