Remove SslHttpClient?

I would like to remove this class and all the code (constructors in ``RemoteDocker``, mostly) that makes any assumption regarding securing communication with a remote Docker instance.

My reasoning is that we shouldn't make any assumptions since we will most likely not cover all the possibilities and we are just polluting the library. If the user really needs it and knows what they are doing, they can provide a properly configured ``HttpClient`` when instantiating a ``RemoteDocker``.

What do you think?