AbstractInputHarvester: make getObjects() not return duplicates

* both the convertService and the objectService attach objects of a
given type to the result list of AbstractInputHarvester:getObjects
* this results into the same objects being in the list twice
* using a set avoids duplicates in the list

src/main/java/org/scijava/widget/AbstractInputHarvester.java

@@ -30,7 +30,9 @@
 package org.scijava.widget;
 
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 
 import org.scijava.AbstractContextual;
 import org.scijava.convert.ConvertService;
@@ -129,10 +131,10 @@ private <T> WidgetModel addInput(final InputPanel<P, W> inputPanel,
 	@SuppressWarnings("unchecked")
 	private List<?> getObjects(final Class<?> type) {
 		@SuppressWarnings("rawtypes")
-		List compatibleInputs =
-			new ArrayList(convertService.getCompatibleInputs(type));
+		Set compatibleInputs =
+				new HashSet(convertService.getCompatibleInputs(type));
 		compatibleInputs.addAll(objectService.getObjects(type));
-		return compatibleInputs;
+		return new ArrayList<>(compatibleInputs);
 	}
 
 }