New feature added to AddSubConf (and AddSub).

AddSubConf and by extension AddSub will now unmarshal previously
loaded JSON into the new config given as argument to these two
methods.

Feature is ment to inspire proper init() usage without worrying
about import and configuration ordering. Importing congo and
loading JSON into it is enough to allow all AddSub(Conf)'s to
be valid and behave as expected without introducing import cycles.