A HEAD to a Container does not return the correct Content-Type

When I do a HEAD request to a Container, I get a Content-Type of application/octet-stream:

$ curl --head https://vincent-test.inrupt.net/public/    
# ...
Content-Type: application/octet-stream; charset=utf-8

even though an actual GET request will return text/turtle:

$ curl --include --request GET https://vincent-test.inrupt.net/public/
# ...
Content-Type: text/turtle

To compare, doing a HEAD to a regular Resource does give me text/turtle:

$ curl --head https://vincent-test.inrupt.net/public/poddit.ttl
# ...
Content-Type: text/turtle; charset=utf-8

$ curl --include --request GET https://vincent-test.inrupt.net/public/poddit.ttl 
# ...
Content-Type: text/turtle

先重現 issue 中顯示的 HEAD 和 GET 請求，然後追蹤伺服器如何處理容器與一般資源，以及如何指派 Content-Type。完成的標準是：針對容器的 HEAD 請求與 GET 一致地回傳 text/turtle，同時一般資源的行為維持不變。