Draft release notes HydPy 6.5

[tyralla]

General features and improvements:

• For each parameter, sequence, and method, the online documentation now lists all application models in which it is used. So far, we have documented the same thing only in the opposite direction. Hence, this change does not really introduce more information to the documentation but simplifies answering questions like "Which models calculate a process in that way" significantly.
• Selection += Selection | Nodes | Elements | Iterable[Node | Element] and -=
• CalibrationInterface.random_values
• Save project settings. #47
• SubmodelProperty/SubmodelProperties: turn submodel interface text into hyperlinks
• Improve/extend submodel-related error messages.