drools-wb screens adpated to illegal transitive dependency check

org.drools.workbench.screens.guided.scorecard.backend.server.GuidedScoreCardEditorServiceImpl

The above class is using Plexus. I am completely unsure of the reasons. From the initial analysis,  looks like the code can be refactored to remove the dependency.

Do let me know if you want me to raise a PR.