Misc code householding

- Checkstyle config: allow todo comments with issue number
- Create consistency tests across all classes, ensuring: unique class names, users of expiring collectors implement HasCleanup, non-private fields are only constants
- Fix tag replacement in PlayerListener for {DISPLAYNAME}

src/main/java/fr/xephi/authme/util/expiring/ExpiringMap.java

@@ -24,7 +24,7 @@ import java.util.concurrent.TimeUnit;
  */
 public class ExpiringMap<K, V> {
 
-    protected final Map<K, ExpiringEntry<V>> entries = new ConcurrentHashMap<>();
+    private final Map<K, ExpiringEntry<V>> entries = new ConcurrentHashMap<>();
     private long expirationMillis;
 
     /**
@@ -105,6 +105,13 @@ public class ExpiringMap<K, V> {
         return entries.isEmpty();
     }
 
+    /**
+     * @return the internal map
+     */
+    protected Map<K, ExpiringEntry<V>> getEntries() {
+        return entries;
+    }
+
     /**
      * Class holding a value paired with an expiration timestamp.
      *

src/main/java/fr/xephi/authme/util/expiring/TimedCounter.java

@@ -44,13 +44,13 @@ public class TimedCounter<K> extends ExpiringMap<K, Integer> {
      * @param key the key to increment the counter for
      */
     public void decrement(K key) {
-        ExpiringEntry<Integer> e = entries.get(key);
+        ExpiringEntry<Integer> e = getEntries().get(key);
 
         if (e != null) {
             if (e.getValue() <= 0) {
                 remove(key);
             } else {
-                entries.put(key, new ExpiringEntry<>(e.getValue() - 1, e.getExpiration()));
+                getEntries().put(key, new ExpiringEntry<>(e.getValue() - 1, e.getExpiration()));
             }
         }
     }
@@ -62,7 +62,7 @@ public class TimedCounter<K> extends ExpiringMap<K, Integer> {
      */
     public int total() {
         long currentTime = System.currentTimeMillis();
-        return entries.values().stream()
+        return getEntries().values().stream()
             .filter(entry -> currentTime <= entry.getExpiration())
             .map(ExpiringEntry::getValue)
             .reduce(0, Integer::sum);