Refactor frankDoc related methods, to be in the FrankDocumentService

[philipsens]

Is your feature request related to a problem? Please describe. There are a lot of functions everywhere to get elements and parents and types and such.

Describe the solution you'd like Place these methods in the service that has been made for it. This should even remove the need for an observer.

Describe alternatives you've considered

• A helper class.
• Extend the functionality of the https://github.com/ibissource/frank-doc to include an extensive REST API.

Additional context Methods must be async for when the FrankDoc hasn't been fetched jet.