Feature: refactoring + delayed post parsing

These changes were driven by the desire to remove the `proxy_mode` flag and delay POST data parsing till it is actually needed by the application thus avoiding a potential DOS scenario.

For this to work we need to move the `connection` into the `HttpContext` record gaining access to read and write to the underlying socket from within a `WebPart`. This in itself opens a world of possibilities in the quest for the perfect API.