Bug 283 import from ocid

Updates to cover initial review comments plus delta importing. Should be ready to start playing with real data now (hopefully?)
I think we don't actually need the index on total_measures for this table. For our own cell table is used in the unthrottling tasks, but we don't run such a job on this table.

The index on created makes sense, so we can add a new stat for the table and plot growth.