Bug Fix Block Size

- Enforce that the specified size of the data matches the actual size of the data when adding a block (both store_block and store_async_block)
- Fix the block put end-point to correctly get the content length even if the caller forgot to specify it so that we have it for the validation (above) and database if everything matches
- Fix Cassandra so that it does not incorrectly register a block
Could you add a comment here, on why we are doing this. It will help whenever we revisit the code next time.