Make edit update search cache

[frankduncan]

Currently when editing a field, the search cache does not get updated (and in fact, the search cache will never reflect the edits). This needs to change, with acceptable time delay. This shouldn't require a background job, but it may.

We shouldn't tackle this until the move to postgres has been completed. This will require looping over all the sheet_configs, and then updating the rows that include the row being edited. We can probably be lazy and do it even for groups that may not have access to this field, as the time hit shouldn't be huge.

This also requires changing the cache generation (for instance, when we change the permissions of a group) to use edit values, rather than natural ones.