rewrote singleton to enum where applicable

Mage.Client/src/main/java/mage/client/deckeditor/SortSettingBase.java

@@ -36,10 +36,10 @@ import mage.client.dialog.PreferencesDialog;
 
 public class SortSettingBase extends SortSetting {
 
-    private final static SortSettingBase fInstance = new SortSettingBase();
+    private final static SortSettingBase instance = new SortSettingBase();
 
     public static SortSettingBase getInstance() {
-        return fInstance;
+        return instance;
     }
 
     private SortSettingBase() {

Mage.Client/src/main/java/mage/client/deckeditor/SortSettingDeck.java

@@ -36,10 +36,10 @@ import mage.client.dialog.PreferencesDialog;
 
 public class SortSettingDeck extends SortSetting {
 
-    private final static SortSettingDeck fInstance = new SortSettingDeck();
+    private final static SortSettingDeck instance = new SortSettingDeck();
 
     public static SortSettingDeck getInstance() {
-        return fInstance;
+        return instance;
     }
 
     private SortSettingDeck() {

Mage.Client/src/main/java/mage/client/deckeditor/SortSettingDraft.java

@@ -36,10 +36,10 @@ import mage.client.dialog.PreferencesDialog;
  */
 public class SortSettingDraft extends SortSetting {
 
-    private final static SortSettingDraft fInstance = new SortSettingDraft();
+    private final static SortSettingDraft instance = new SortSettingDraft();
 
     public static SortSettingDraft getInstance() {
-        return fInstance;
+        return instance;
     }
 
     private SortSettingDraft() {

Mage.Client/src/main/java/mage/client/deckeditor/SortSettingSideboard.java

@@ -36,10 +36,10 @@ import mage.client.dialog.PreferencesDialog;
 
 public class SortSettingSideboard extends SortSetting {
 
-    private static final SortSettingSideboard fInstance = new SortSettingSideboard();
+    private static final SortSettingSideboard instance = new SortSettingSideboard();
 
     public static SortSettingSideboard getInstance() {
-        return fInstance;
+        return instance;
     }
 
     private SortSettingSideboard() {

Mage.Client/src/main/java/mage/client/plugins/impl/Plugins.java

@@ -35,7 +35,7 @@ public class Plugins implements MagePlugins {
 
     public static final String PLUGINS_DIRECTORY = "plugins/";
 
-    private static final MagePlugins fINSTANCE = new Plugins();
+    private static final MagePlugins instance = new Plugins();
     private static final Logger LOGGER = Logger.getLogger(Plugins.class);
     private static PluginManager pm;
 
@@ -46,7 +46,7 @@ public class Plugins implements MagePlugins {
     private final Map<String, String> sortingOptions = new HashMap<>();
 
     public static MagePlugins getInstance() {
-        return fINSTANCE;
+        return instance;
     }
 
     @Override

Mage.Client/src/main/java/mage/client/unusedFiles/DelayedViewerThread.java

@@ -9,10 +9,10 @@ import java.util.Map;
 
 
 public class DelayedViewerThread extends Thread {
-    private static final DelayedViewerThread fInstance = new DelayedViewerThread();
+    private static final DelayedViewerThread instance = new DelayedViewerThread();
 
     public static DelayedViewerThread getInstance() {
-        return fInstance;
+        return instance;
     }
 
     private final Map<Component, Long> delayedViewers;

Mage.Client/src/main/java/mage/client/util/GameManager.java

@@ -8,10 +8,10 @@ import java.util.UUID;
  * @author nantuko
  */
 public class GameManager {
-    private static final GameManager fInstance = new GameManager();
+    private static final GameManager instance = new GameManager();
 
     public static GameManager getInstance() {
-        return fInstance;
+        return instance;
     }
 
     public void setStackSize(int stackSize) {

Mage.Client/src/main/java/mage/client/util/SettingsManager.java

@@ -10,10 +10,10 @@ import org.mage.card.arcane.CardPanel;
  * @author nantuko
  */
 public class SettingsManager {
-    private static final SettingsManager fInstance = new SettingsManager();
+    private static final SettingsManager instance = new SettingsManager();
 
     public static SettingsManager getInstance() {
-        return fInstance;
+        return instance;
     }
 
     public int getScreenWidth() {

Mage.Client/src/main/java/org/mage/plugins/card/utils/impl/ImageManagerImpl.java

@@ -19,10 +19,10 @@ import org.mage.plugins.card.utils.Transparency;
 
 public class ImageManagerImpl implements ImageManager {
 
-    private static final ImageManagerImpl fInstance = new ImageManagerImpl();
+    private static final ImageManagerImpl instance = new ImageManagerImpl();
 
     public static ImageManagerImpl getInstance() {
-        return fInstance;
+        return instance;
     }
     
     public ImageManagerImpl() {