enable multiprocessing termination mid-run from app.py

[justinhchae]

Is your feature request related to a problem? Please describe.
stopping spawned multiprocesses from app.py is a big problem. requires terminal ^C and complete script restart

Describe the solution you'd like
enable app user to terminated spawned mps during app run

Describe alternatives you've considered
not sure

Additional context
Add any other context or screenshots about the feature request here.