Move table rotation logic to separate class and improve resilience

- For sheer massive file reasons, move code out of DynamoManager and
  reorganize the code that is left.
- Refactor the table rotation code for clarity and testability.
- Rotation code now blocks until table is ready for writing. If there's a
  delay, the current table is not rotated out, so things should work fine.
- Increase table creation headroom to 60s, to match real Dynamo performance.
Remove repositories stanza and add gpg plugin, for deployment to central.