Eliminated setting the display 2x when a selected artifact is found; removed always false check for ArtifactStringContent object in Lookup of selected node
Merge remote-tracking branch 'upstream/master' into artifact_viewer_thread
Added worker thread to do display for DataContentViewerArtifact
Merge pull request #267 from rcordovano/artifact_viewer_thread

Reduced work done by DataContentViewerArtifact objects