Conditional hidden family and calculated default value

Add a sub family "https_proxy" which will be hidden if "use_for_https" is True.

Hidden means that we cannot change value, but we can access to it in read only mode. Inside, we add two variable with calculated default value (with variable type).

So, if user set "use_for_https" to True, the default values of HTTPS configuration will be a copy of HTTP values. The use can change HTTPS values if needed.

If user set "use_for_https" to False, the default values of HTTPS configuration will only be a copy of HTTP values.
