Image-dataset-converter

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- limiting numpy to <2.0.0 due to problems with imgaug library

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- switched to the `fast-opex` library
- helper method `from_indexedpng` was using incorrect label index (off by 1)
- `Data.save_image` method now ensures that source/target files exist before calling `os.path.samefile`
- requiring seppl>=0.2.6 now
- readers now support default globs, allowing the user to just specify directories as input
(and the default glob gets appended)
- the `to-yolo-od` writer now has an option for predefined labels (for enforcing label order)
- the `to-yolo-od` writer now stores the labels/labels_cvs files in the respective output folders
rather than using an absolute file name
- the bluechannel/grayscale/indexed-png image segmentation readers/writers can use a value other
than 0 now for the background
- `split` filter has been renamed to `split-records`

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- added generic plugins that take user Python functions: `from-pyfunc`, `pyfunc-filter`, `to-pyfunc`
- added `idc-exec` tool that uses generator to produce variable/value pairs that are used to expand
the provided pipeline template which then gets executed
- added `polygon-simplifier` filter for reducing number of points in polygons
- moved several geometry/image related functions from imgaug library into core library to avoid duplication
- added python-image-complete as dependency
- the `ImageData` class now uses the python-image-complete library to determine the file format rather than
loading the image into memory in order to determine that
- the `convert-image-format` filter now correctly creates a new container with the converted image data
- the `to-coco-od` writer only allows sorting of categories when using predefined categories now
- the `from-opex-od` reader now handles absent meta-data correctly
- added the `AnnotationsOnlyWriter` mixin for writers that can skip the base image and just output the annotations

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- initial release