Merge pull request biolab#1812 from janezd/scatterplot-label-strings

[FIX] Scatterplot: Allow labelling by string attributes
(cherry picked from commit 002981b)

Orange/widgets/visualize/owscatterplot.py

@@ -198,7 +198,7 @@ def __init__(self):
             callback=self.update_colors,
             model=self.color_model, **common_options)
         self.label_model = DomainModel(
-            placeholder="(No labels)", valid_types=dmod.PRIMITIVE)
+            placeholder="(No labels)")
         self.cb_attr_label = gui.comboBox(
             box, self, "graph.attr_label", label="Label:",
             callback=self.graph.update_labels,