Add boilerplate code for replacing test server.

@lunaryorn I could use your help here. I've given up using the server built-in to Servant. It's too unstable, crashes all the time, only works on snapshot, etc...

I could write a server in Node or Ruby myself, but since both `bin/cask` and `go` is written in Python, I figured it would be best to write the test server in Python as well.

For now, I simply cd to the `servant` directory and run this to start the server:

```bash
$ python -m SimpleHTTPServer 9191
```

But this will not work on Travis since we have to run it in the background and preferably kill the server when done.

I could try and write the server myself, but I guess what will take me a long time, will be a no-brainer for you.  As you see from the PR, all the boilerplate code is already setup. The only thing left is to fill in the blanks in `servant/server`.

As I mentioned, for now it works by starting the server manually, it's only Travis that will be an issue, so there's no rush.

Do you think you could help me out with this?

Thanks!