Support authentication and security stuff

Here's the comment from Solomon Shykes in HN.

Everything you say is true, but it doesn't mean this web ui is not useful, or a bad idea. It just means that it should add authentication :)

Since we are developing Docker's identity and authentication primitives separately from the main binary (https://github.com/docker/libtrust), it would be a cool experiment to try using that in Seagul.

Personally I think this is a cool project, and look forward to seeing it evolve!

Now seagull is kind of for developers. We don't consider about security a lot. Maybe we should know more about libtrust and try to support authentication.