Deprecate all usages of HttpConnector and HttpURLConnection

[bitwiseman]

HttpConnector depends on HttpURLConnection an old and very crufty way of working with Http connections. Some modern clients have even stopped supporting HttpURLConnection. This makes it harder to implement support for different http clients.

We should remove all dependency on HttpConnector. GithubClient will become the new base class to extend in order to support new clients. Other methods the depend on HttpURLConnection should switch to other ways of providing the same information.

[bitwiseman]

The implementation details changed but this task is complete.