Fix sort key/range key ordering in dynamodb events table

[chriscosgriff]

PR #110 correctly removed the commitStamp from the derived rowKey value in the dynamodb provider to resolve a concurrency issue, however it has also revealed an issue with the events table sort key/range key (provided by the derived "rowKey" value)

Queries/Scans against aggregates with more than 10 revisions are currently being returned with an incorrect sort order from the dynamodb events table due to the stream revision value not being padded.

e.g. (current)

aggregateId	rowKey
myagg1	::0
myagg1	::1
myagg1	::10
myagg1	::2
myagg1	::3
...
myagg1	::9

e.g. (with fix by padding the stream revision value during rowKey derivation)

aggregateId	rowKey
myagg1	::000
myagg1	::001
myagg1	::002
myagg1	::003
...
myagg1	::009
myagg1	::010

I have set the padding amount to 16 digits, which represents the number of digits in the Number.MAX_SAFE_INTEGER value.