Create Cell Area Table (#349)

- Create CellArea table
- Add model tests
- Migrate cell area data from cell table to cell_area
- Change references from Cell table to CellArea table

@hannosch 
Please remove the compressed/key_block_size from this one. We used compression early on in the project, but it doesn't actually help much and actually hurts small and frequent updates, as a larger compressed block has to be updated each time, and not just the specific row.