Initial attempts to migrate EFMissingETFromCells

...rithms/TrigEFMissingET/TrigEFMissingET/EFMissingETAlgMT.h

.../TrigEFMissingET/TrigEFMissingET/EFMissingETFromCellsMT.h

...TrigEFMissingET/TrigEFMissingET/EFMissingETFromHelperMT.h

...gorithms/TrigEFMissingET/TrigEFMissingET/IMissingETTool.h

Trigger/TrigAlgorithms/TrigEFMissingET/share/testMET.py

...r/TrigAlgorithms/TrigEFMissingET/src/EFMissingETAlgMT.cxx

...Algorithms/TrigEFMissingET/src/EFMissingETFromCellsMT.cxx

...lgorithms/TrigEFMissingET/src/EFMissingETFromHelperMT.cxx

...rigEFMissingET/src/components/TrigEFMissingET_entries.cxx

...ger/TrigAlgorithms/TrigEFMissingET/test/test_met_fexes.sh