Create OCIDCellArea #348

- Create OCIDCellArea table/model
- Change update_lac to accept arbitrary models
- Change enqueue/dequeue LACs to accept arbitrary pipelines (not presently used)
- Populate with LACs on OCID import
- Add tests for OCIDCellArea Model
- Update OCIDCell import tests to test for the presence of OCIDCellArea entries after import

@hannosch 
Isn't this duplicating the MODEL_KEYS lookup, since we later do `MODEL_KEYS[cell_model_key]`. Why not just use 'cell' and 'cell_area' as the default values for the cell_model_key/cell_area_model_key keyword arguments?