[Vision] Optimise cv_demo python model for Trident

[OscarSmiley]

Background

cv_demo code designed as a demo. However this demo code performs better than previous computer vision code for Polaris

Overall goal

Convert and optimise computer vision code for use in an object detector module on the Jetson

This ticket

Optimise and refactor python code for production without investigating architectural improvements such as threading and multiprocessing yet.