Dependency graphs for API methods

@gdenayer suggested that we should specify what needs to be called before what. This is a rather common request that could indeed improve the documentation a lot.

Triggered by this, @fsimonis added some workflows in the revamped API documentation in https://github.com/precice/precice/pull/1916, which will appear in the Doxygen documentation. Maybe we could reference / link these dependency graphs also from the "couple your code" page.