Add a Python script that can run in all supported platforms, and can
download and extract the Tesseract language data from GitHub, while
also:
1. Checking that the expected hash matches.
2. Informing the user if the language data have already been downloaded.
3. Extracting only the subset of language data that Dangerzone needs
As a result, a new `debian` folder is now living in the repository.
Debian packaging is now done manually rather than using tools that do
the heavy-lifting for us.
The `build-deb.py` script has also been updated to use `dpkg-buildpackage`
Ensure that when the container image is installing pymupdf (unavailable
in the repos) with verified hashes. To do so, it has the pymupdf
dependency declared in a "container" group in `pyproject.toml`, which
then gets exported into a requirements.txt, which is then used for
hash-verification when building the container.
Because this required modifying the container image build scripts, they
were all merged to avoid duplicate code. This was an overdue change
anyways.
