Clean up Core Entities

[ThePhisch]

Description

Some core entities such as the ones stored in https://github.com/rucio/webui/blob/5cf28d4575d62600bca5d97856df27518b7e2a85/src/lib/infrastructure/data/view-model/page-did.d.ts are not in the appropriate folder lib/core/entity

[maany]

@MytsV this refactor is independent of the UI and framework changes. Could you pick it up already :)

[MytsV]

@MytsV this refactor is independent of the UI and framework changes. Could you pick it up already :)

Sorry, sometimes procrastination is about avoiding the easier tasks XD

[MytsV]

The commit that seemingly did all of the refactoring is mentioned in #320. There's a bit of chaos in the view-model/create-rule.ts, but it might be better to review it while working on finishing off the Create Rule page