Add selectedIDs() for modeMove and modeRotate

This allows the label collision boxes for the vertices to update
during these modes. Otherwise the labels.js `isInterestingVertex()`
function doesn't consider them interesting enough to update.

modules/modes/move.js

@@ -192,5 +192,12 @@ export function modeMove(context, entityIDs, baseGraph) {
     };
 
 
+    mode.selectedIDs = function() {
+        if (!arguments.length) return entityIDs;
+        // no assign
+        return mode;
+    };
+
+
     return mode;
 }

modules/modes/rotate.js

@@ -155,5 +155,12 @@ export function modeRotate(context, entityIDs) {
     };
 
 
+    mode.selectedIDs = function() {
+        if (!arguments.length) return entityIDs;
+        // no assign
+        return mode;
+    };
+
+
     return mode;
 }