valueRangeProvider: improve error message
javadocs
PLANNER-160: ValueRange interface prototype + IntValueRange + test
PLANNER-160: ListValueRange + test
PLANNER-160: comment
PLANNER-160: CompositeValueRange
javadoc
PLANNER-160: NullableValueRange
PLANNER-160: NullableValueRange
PLANNER-160: hook in the ValueRange's into the Selectors and Descriptors