Split base class observables

Draft: Split base class observables

Allows user to place BeamObservationInPipeline as an element at a specific location in the ring.

Now BeamPhysicsRelevant and BeamObservationElement inherit from SimulationElementBase.

Added BeamObservationInPipeline inside handle_results/observables_as_elements.py inheriting from base classes BeamObservationElement, ObservablesGeneralElement

Changed class structure in handle_results/observables.py to bases ObservablesGeneralElement and ObservablesEndOfTurn which inherits from ObservablesGeneralElement.

Does not work with sim.from_locals()