OpenMW-CS: Handle changes to cells and references
Currently modifications to cells and references are not correctly implemented. During loading references are flattened into a single table, but the table keeps a list of the IDs. When references are modified, the table needs to be updated. Likewise when the table is modified (e.g. deleted), the respective references must be updated.
As a part of this task saving of cell records (which include the references) should also be implemented.