Handle HEAD requests

[kappsegla]

When asking for a file using GET as method in the request we send first a header as response and then we send the actual file as bytes.
When someone uses HEAD as method in a request for a file or resource on the server we should process it as for a GET but with the exception that we only send the header as a response not the actual data.
The header should still contain Content-type and Content-length as for get but without sending the file.