WIP: dev for serial merging in HLT menu (ATR-19824)

development for serial merging in the HLT menu has two steps:

• create EmptyMenuSequence class, which ensures connections between filters in steps (see MenuComponents.py)
• test one chain in the emulation test having one ChainStep, containing one EmptyMenuSequence see Trigger/TrigValidation/TrigUpgradeTest/python/EmuStepProcessingConfig.py by running test_emu_step_processing.sh

This EmptyHypoNode needs several components:

• an Alg which I set to None (and bypassed all references to the hypo name which is need throughout the code)
• an interface for input and output Props (which I bypassed)
• and interface to add outputs (since this is also done elsewhere) and access previous decisions from the inputs (incase the chain has already failed one of the previous serial steps) and to read the outputs (this is where the CF gets the information to pass information through)

However this still doesn't run since different sections of the code (CFSequence, ChainStep, ComboMaker etc) read information from different nodes of the standard menu sequence interface. To the EmptyMenuSequence I added:

• EmptyHypoNode (as above)
• Maker node (Similar to empty but with a different alg)
• a Sequence Node (I just made another dummy Alg = None bypass)
• an interface connectToFilter which links the interfaces (and contains most of my Alg info bypasses)
• a "getter" for the empty hypo.

• test one chain in the emulation test having one ChainStep, containing one EmptyMenuSequence see Trigger/TrigValidation/TrigUpgradeTest/python/EmuStepProcessingConfig.py by running test_emu_step_processing.sh

Tagging @fpastore @markowen @jmontejo