Write configuration files using UTF-8 encoding (detected during CONTROLGUI-380)

src/main/java/fr/soleil/comete/bean/trend/controller/CometeTrendController.java

@@ -3,8 +3,10 @@ package fr.soleil.comete.bean.trend.controller;
 import java.awt.Color;
 import java.awt.Component;
 import java.io.File;
-import java.io.FileWriter;
+import java.io.FileOutputStream;
 import java.io.IOException;
+import java.io.OutputStreamWriter;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashMap;
@@ -187,7 +189,8 @@ public class CometeTrendController {
                     JOptionPane.YES_NO_OPTION);
         }
         if (ok == JOptionPane.YES_OPTION) {
-            try (FileWriter writer = new FileWriter(fileName)) {
+            try (OutputStreamWriter writer = new OutputStreamWriter(new FileOutputStream(fileName),
+                    StandardCharsets.UTF_8)) {
                 writer.write(chartConfiguration);
             }
         }