Python3 and flake8 fixes for G4Extensions packages

This merge request replaces usage of dict.has_key(KEY) with KEY in dict.
Additionally it adds flake8 checks for G4Extensions packages and fixes any warnings found.
Should fix ATLASSIM-4663.

This merge request affects 9 packages:

• Simulation/G4Extensions/Charginos
• Simulation/G4Extensions/ExtraParticles
• Simulation/G4Extensions/G4CosmicFilter
• Simulation/G4Extensions/G4HitFilter
• Simulation/G4Extensions/G4ScoringProcess
• Simulation/G4Extensions/Gauginos
• Simulation/G4Extensions/Monopole
• Simulation/G4Extensions/Quirks
• Simulation/G4Extensions/Sleptons

Adding @jchapman ,@vpascuzz as watchers

added Simulation master review-pending-level-1 labels

changed the description

CI Result SUCCESS (hash a46557a2)

	Athena	AthSimulation	AnalysisBase	AthGeneration
externals
cmake
make
required tests
optional tests

Full details available on this CI monitor view
Athena: number of compilation errors 0, warnings 0
AthSimulation: number of compilation errors 0, warnings 0
AnalysisBase: number of compilation errors 0, warnings 0
AthGeneration: number of compilation errors 0, warnings 0
For experts only: Jenkins output [CI-MERGE-REQUEST-CC7 17341]

added review-approved label and removed review-pending-level-1 label

merged

mentioned in commit 8b1ce6b4

added sweep:ignore label

mentioned in merge request !35422 (merged)