Fixed removeListener issue + partial implementation of ?

src/main/java/data/CorpusType.java

@@ -1,5 +1,8 @@
 package data;
 
+import java.util.ArrayList;
+import java.util.Arrays;
+
 public enum CorpusType {
 	GIGAFIDA("Gigafida", "gigafida"),
 	GIGAFIDA2("Gigafida2.0", "gigafida2.0"),
@@ -25,4 +28,8 @@ public enum CorpusType {
 	public String getNameLowerCase() {
 		return nameLowerCase;
 	}
+
+	public static ArrayList<CorpusType> multipleFilesCorpuses() {
+		return new ArrayList<>(Arrays.asList(new CorpusType[]{GIGAFIDA, GIGAFIDA2, CCKRES}));
+	}
 }