Core: drop [get|set]ChildTopicValue() (#339, #411)

BREAKING CHANGES

DeepaMehtaObject (interface):
    - SimpleValue getChildTopicValue() is dropped
    - void setChildTopicValue()        is dropped

CompositeValue (interface):
    - void set(String childTypeUri, SimpleValue value, ClientState clientState, Directives directives) is new method

To adapt your plugins, replace
{{{
    object.getChildTopicValue("child.type.uri")
}}}
with
{{{
    object.getCompositeValue().getTopic("child.type.uri").getSimpleValue()
}}}

Replace
{{{
    object.setChildTopicValue("child.type.uri", new SimpleValue(val))
}}}
with
{{{
    object.getCompositeValue().set("child.type.uri", new SimpleValue(val), clientState, directives)
}}}

Furthermore: CompositeValue's getTopic() and getTopics() methods do fetch the respective child topics lazily.

See ticket 339.
See ticket 411.