Crop and resize to optimum image size if using bounding box ROI

[robmarkcole]

Deepstack allows setting mode High , Medium and Low, where the default mode is Medium. It can be seen at https://github.com/johnolafenwa/DeepStack/blob/5c59bee5fc92b2c793dcacd61942727b1d2ed38f/intelligencelayer/shared/shared.py#L62 the choice of mode dictates the resizing of input images. In order for best results (maintaining image resolution) we should crop images to the maximum size permitted. So if for example an HD camera is used with an approriate ROI, there would be no downgrading of the image on processing if we resize correctly. However the implementation of this feature would be complex, since the max sizes vary for jetson and other platforms.

[wizmo2]

@robmarkcole I add PR #271 as an intermedate solution. It doesn't perform checks on sizes, but does improve performance when you are using only small ROIs.

Great integration BTW.