We need to add a topic attribute to the manifests. This task includes:

• Add topic attribute to specification and adapt validator to allow topic attribute as optional parameter. The validator should report missing topics as a warning, but not fail
• Add list of allowed topics to the validator, Topics not being in this list should be reported as error
• Adapt rendering of the library pages to include topics
• Add topics to manifests. Use https://github.com/cornelius/inqlude/blob/master/topics/topics.csv as a base