Remove limitation of 1000 rows for snapshots

[proehlen]

Limit was added initially as a quick fix for performance. Snapshotting more than 1000 rows is not a problem so much as diffing several thousands of rows.

Options include:

1. allow user to set limit with adequate warning about performance.
2. add snapshot filter capability that can be used to equally reduce number of records in snapshots that are produced and also then applied to db records when diffing.