Introduce a templated animationTime overload for the KConfigXT case

This method can be used to get the animationTime in case a configuration
class generated through KConfigXT is used. In general the configuration
stores the magic value 0 for a property "duration". This magic value
indicates that a hard-coded default value should be used.

So the common logic to test the stored value for 0 and then either pass
the stored value or the default value to animationTime is encapsulated
in this method in a generic way.

A MyEffect can use it in the following way:
animationTime<MyEffectConfig>(200);


FIXED-IN: 4.10
REVIEW: 107460