missing licence for bundled schema files

[karenetheridge]

The JSON Schema and OpenAPI projects require that redistribution of their schema files include a valid licence (which can be obtained from their github repositories).

The lack of licence is also causing downstream packaging issues - see https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1091856

[briandfoy]

This is a good opportunity to fix #270 :)