Add custom OCR engines

[GrimPixel]

Currently the version of supported Tesseract is 4.1.1, which is already another legacy version. It would be best to let users download engines and use them.

[mathewthe2]

I can see use cases with Tesseract5, manga_ocr, and paddle ocr.

It's pretty straightforward to include them in the build, but it will introduce lots of dependencies, greatly increasing the size and weight of the app.

For optional downloads, however, it will require making separate binaries for the user to easily download and use them. I will get back if I manage to package them or if someone can supply them.