Validate JSON files using JSON schema

[vasdommes]

We have JSON schemas e.g. for sdpb input files, e.g. docs/sdpb_input_block_schema.json.
We can use schemas to check correctness of both schemas and serialization code.

• Validate in integration tests (should be easy)
• Validate inside a program (a bit harder, since we have to save schemas to executable during compilation)