Use Thread Pool

[gfiumara]

Is your feature request related to a problem? Please describe.
Multi-threading in NFIQ2 first splits the input workload into N parts and then launches N threads.

Describe the solution you'd like
Launch N threads and have them each each be available for work without starvation

Describe alternatives you've considered
No change.

Additional context

• Large datasets may require a long period of waiting and a large amount of RAM to separate up the input workload.
• This would allow directory contents to be multithreaded without making a list of all files first.