Evaluate need for additional marker annotation for CustomServiceTasks

When inspecting JAR files, the annotations of the IType can be read as opposed to the type hierarchy. An additional annotation would allow for early separation of concrete CustomServiceTask implementations (i.e. skipping any class without the annotation) and therefore speed up the inspection. This is a trade-off with developer ease because it would require the usage of an extra annotation. It might not be required if we can solve other related issues.