Manifest file sections are fixed

[danutza77]

Need to make sure that the defined sections of the sdv-manifest.toml are fixed.
E.g. in case the are no licenses.md files, the resulting sdv-manifest.toml file should still contain a "licenses" section even though it will be empty.

[AnotherDaniel]

Can I asked why this needs to be the case? Or maybe put differently: with the quevee v2 json output format (#13 ), would this also be necessary? Tools like jq should be able to manage just fine, even without fixed empty sections...