Allow the exclusion of individual concepts/constraints from an included group

[SebastianWendorf]

The excluded concepts/constraints have to be part of the included group and should not be executed. Conflicting declarations, like the inclusion in one place and the exclusion in another place should lead to an error/warning.

Example:

<group id="default">
    <includeGroup refId="plugin:SomeGroup">
        <excludeConcept refId="plugin:SomeConcept"/>
        <excludeConstraint refId="plugin:SomeConstraint"/>
    </includeGroup>
</group>