Script should do the following

• Validate the links of the podcasts (whether they are broken)
• Validate the order of the podcasts in each category (and also categories)

Break the build when either of the above validations fail

Coordinate with #1133 and #1137

Description of issue or feature request:
For consistent use of OOP we should provide classes for all complex metadata fields
and not only for the outer metadata signature wrapper and the inner signed metadata.

This would make the used metadata format more explicit and might have a positive effect on metadata schema validation (see discussion in #1130)