Move Reservoir object serialization to different class

User Story: As a user of datamodel.io, the ReservoirSchema should cater for needs of both RAMSIS and the worker. A bug was found when used by RAMSIS. There are two formats which a reservoir is expected as, an editable MutableDict by the RAMSIS gui and a ReservoirGeometryEdges object, but the requirement for a MutableDict had been missed. I propose to move the object serialization to a class that inherits.

Acceptance criteria: A normal workflow in RAMSIS and the worker/sfm_models is completed successfully with the reservoir objects loaded into the correct format for each purpose. This should contain setup steps in RAMSIS gui and end with successful retrieval of data from model.

Alterations will be required in RAMSIS to alter io class used.