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 
This might be more generally useful, so maybe put it in models.py?