Get object metadata

[koenedaele]

Currently, you always need to download an object to find out more about it. To make it possible to save some bandwith, we will implement the HEAD method for objects.

[koenedaele]

Please implement this in branch head_for_objects.

Basic idea is to return the Content-Type and Content-Length without actually sending the object itself. This allows a client to check a file's size without having to download the entire file all the time. At this moment i'm not sure if this needs to be new methods on the Store interface or just the server getting the object and only sending the metadata. To keep things simple I would suggest that for now we just get the object from the store, but don't send it.

[koenedaele]

Doesn't really need to be implemented since Pyramid automatically adds a HEAD method to a resource that returns the same headers a GET, but without the body. While this still requires Augeias to fetch the entire object from storage, it does not require sending the object over the wire. So, that's a plus.