Deprecate WebRequest and related classes.

Current implementation is completely broken. It's not compatible with Servlet filters that calls  `HttpServletRequest#getParameter(String)`.

Once a filter calls `HttpServletRequest#getParameter(String)`, it eats content body from `HttpServletRequest#getInputStream()`. Then, the Servlet can't read parameters...

Servlet application shouldn't try to parse the application/x-www-urlencoded and multipart/form-data!