Refactor frankDoc related methods, to be in the FrankDocumentService

**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.