Relax requirement for size argument during blob upload

During client implementation, it was found that requiring the size argument
made client implementation more complex. The original benefit of the size
argument was to provide an additional check alongside of tarsum to validate
incoming data. For the purposes of the registry, it has been determined that
tarsum should be enough to validate incoming content.

At this time, the size check is optional but we may consider removing it
completely.
Port client to use URLBuilder to create urls

This change ports the client use the URLBuilder to create urls. Without this,
it produces broken urls for certain use cases. The client has also been updated
to no longer use the size argument to complete blob uploads. Much of this work
has been done after testing with the staging registry instance.
Merge pull request #848 from stevvooe/next-generation

Relax requirement for size argument during blob upload