NIFI-1027 - Treat label and node of a provenance graph event as one unit

The JIRA issue asks for treating both node and its label as one unit.
Described cursor issues seems to be fixed already.

However, there is an annoying dead space between a node and label
preventing displaying context menu, etc. Due to SVG group's nature
there has been added an opaque joint to remove the dead space.

Signed-off-by: Pierre Villard <pierre.villard.fr@gmail.com>

This closes #2059.

nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-web/nifi-web-ui/src/main/webapp/js/nf/provenance/nf-provenance-lineage.js

@@ -1019,6 +1019,20 @@
 
                 events
                     .classed('event', true)
+                    // join node to its label
+                    .append('rect')
+                    .attr({
+                        'x': 0,
+                        'y': -8,
+                        'height': 16,
+                        'width': 14,
+                        'opacity': 0,
+                        'id': function (d) {
+                            return 'event-filler-' + d.id;
+                        }
+                    });
+
+                events    
                     .append('circle')
                     .classed('selected', function (d) {
                         return d.id === eventId;