Be more lenient about permissible batch spec structure

Created by: eseliger

Before, the editor and fromRaw endpoints would constantly throw validation errors while the user is typing in the editor, because on: is interpreted as on: null. As we don't require on, this is just as valid, though. Now, this won't cause schema validation errors anymore. Also, this makes it easier to comment out parts of the spec without breaking validation. I had to update the schema generator a bit, so it would still generate the correct go code. Therefore, I pinned the new version in the gen script, so there won't be any flakes in CI.