Improvements to consumed capacity parsing

[firenero]

Additions:

1. Exposed consumed capacity high-level API for batch requests. Addresses No way to set ReturnConsumedCapacity for BatchGet and BatchWrite requests using builders #222.

Bugfixes:

1. ConsumedCapacity was not parsed at all for DeleteItem operation due to incorrect JSON name mapping.
2. TransactWrite returns a list of consumed capacities (one item per table) but the previous version mapped it to a single item. This is technically a breaking change because it changes public property. However, attempts to get consumed capacity data for TransactWrite always resulted in a crash, so this should not break any real users.
3. Table property in FullConsumedCapacity was not mapped from JSON in all operations.