This commit converts the license handling to adhere to the REUSE
specification. It specifically:
1. Adds used licnses to LICENSES/ directory
2. Add "isc" template for adding the copyright boilerplate
3. Changes all source files to include copyright and SPDX license
header, this includes all the C sources, documentation, zone files,
configuration files. There are notes in the doc/dev/copyrights file
on how to add correct headers to the new files.
4. Handle the rest that can't be modified via .reuse/dep5 file. The
binary (or otherwise unmodifiable) files could have license places
next to them in <foo>.license file, but this would lead to cluttered
repository and most of the files handled in the .reuse/dep5 file are
system test files.
- Add quotes before and after zone name when generating "addzone"
input so avoid "unexpected token" errors.
- Use a hex digest for zone filenames when the zone or view name
contains a slash.
- Test with a domain name containing a slash.
- Incidentally added 'catzhash.py' to contrib/scripts to generate
hash labels for catalog zones, as it was needed to write the test.
