Add BlobWriteOption to support MD5 and CRC32C checks on create/write

[mziccard]

This PR fixes #267. Main changes are:

• Add BlobWriteOption with support for md5Match and crc32cMatch
• Add MD5 and CRC32C computation to create(blobInfo, content, options)
• Change BlobTargetOption... to BlobWriteOption... in create from stream writer
• Update unit tests
• Update and add integration tests

To note that md5Match and crc32cMatch are boolean options always true. If not specified storageobject's crc32c and md5 fields are set to null (so no validation occurs).
Alternatives to boolean options were:

• String options implicitly taken from BlobInfo: this would have required to modify storage.optionMap, that is now used to fetch implicit values only for (meta)generation matches. (meta)generation options are shared across all APIs, so I felt like md5Match and crc32cMatch did not fit here.
• String options explicity set by the user (e.g. BlobWriteOption.md5Match("7uyg8yg8==")), still a valid option but a bit counter-intuitive: all values set in BlobInfo are transmitted, why not to use md5 and crc32c fields?

Comments are appreciated!

[mziccard]

Fixed the comments. I removed options from the RPC layer.
I don't like so much using Tuple for the PRC layer in the BlobTargetOption.convert method I added, what do you think?

[aozarov]

I don't like so much using Tuple for the PRC layer in the BlobTargetOption.convert method I added, what do you think?

Honestly, I wished Tuple was part of the JDK (or at least guava) but I understand the opposition for it.
I am fine with it the way it and as this that is internal we can always be changed later.
If you feel better you can write a dedicate private inner class for it or pass a BlobInfo.Builder.

[mziccard]

@aozarov I don't like the idea of doing side effects on a builder either, lets keep it as is, we can possibly change it later.

[mziccard]

Removed the unnecessary final