Implement optimistic locking #8

[danieljurek]

• No more bulk operations for CUD, using async tasks instead
• Removing entities also respects version field
• Update caching behavior to handle partial failure in optimistic locking scenario

[danieljurek]

[Discussion belongs in the PR, not on the issue] Andy and I work together and I'm helping with this PR.

The PR brings up a few things I want to make sure fit into the design moving forward:

• If a CUD operation fails we'll get an AggregateException with a ConditionalCheckFailedException but no detail about the entity for which the check failed. We should probably create our own exception for this.
• TableDefinitionWrapper has more complex add/update behavior.. We could probably put the responsibility of generating OperationConfigs in a different class.
• We mutate an EntityWrapper's document in the CUD operation. There may be a better way to propagate document changes back to the entity.

[danieljurek]

Was away for a while. Will have an updated PR soon.