Return null from loadSession if the manager is not ready yet.

- We shouldn't get into this state anyway, but hey.
Drop unused return val
Add optional statsd client for tracking request sizes and times.
Switch table name to something human readable (date formatted)
Add extra logging on deserialization errors
Refactor table detection/creation at server startup

- Attempt to find an active table even if it is not the current table
- If none found, create and wait for a table
- Refactor isActive() and isWritable() out of waitForTable()
Catch deleted previous table, treat as session not found.

Refs EnergyHub Trac #10991
Remove old dynamo jars before deploying locally