Refactor to include buffer based ignore regions and remove requirement on...

Refactor to include buffer based ignore regions and remove requirement on kwcoco files for non-image based methods.

I did end up deciding to MR this. I've reorganized a lot of the predict.py code. Big changes are:

1. If you are using "box" or "ellipse" there is no longer any requirement to have a kwcoco file as you don't need images
2. You can specify an "ignore_buffer" to put ignore regions around each polygon.
3. I moved imports into the functions they are used in. This drastically increases response time of the CLI.