Support RFC 3230/5843 Digest Headers in CMIS contentStream operations

Sometimes content streams get corrupted over the wire. Content stream hashes are often used to protect against these corruptions.
Update nuxeo-chemistry to validate contentStream input to AtomPub and Browser Binding CMIS operations, including setContentStream, appendContentStream, checkIn, and createDocument, by comparing the content stream digest against an RFC 3230/5843 "Digest" request header if present. The code should throw a CMIS invalidArgument exception if the hashes are not equal. Also enhance getContentStream CMIS operation to support RFC 3230 "Want-Digest" request header by setting the appropriate "Digest" or "Content-MD5" response header.

https://www.ietf.org/rfc/rfc1864.txt
https://www.ietf.org/rfc/rfc3230.txt
https://www.ietf.org/rfc/rfc5843.txt