Enhancement block storage controller head object

Adds support to HEAD a block through the Storage Block Controller

DEPENDS: PR #166 
Correct. GET does return it, but under the header "Content-Length", which as there is no body here is not appropriate to use. Though I guess I could have used X-Content-Length.

This was in part to be consistent with Storage Block HEAD; I wanted to try to have them return the same things...

Q: I added an X-Block-Orphaned to the Storage Block HEAD, does it make sense to do so here too? I'm thinking not since it would always be "TRUE" for the normal method, or a 404 which doesn't find it at all.