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/test/java/fr/xephi/authme/util/expiring/ExpiringMapTest.java

@@ -76,7 +76,7 @@ public class ExpiringMapTest {
         map.removeExpiredEntries();
 
         // then
-        Map<Integer, ?> internalMap = map.entries;
+        Map<Integer, ?> internalMap = map.getEntries();
         assertThat(internalMap.keySet(), containsInAnyOrder(64, 25));
     }
 

src/test/java/fr/xephi/authme/util/expiring/TimedCounterTest.java

@@ -56,8 +56,8 @@ public class TimedCounterTest {
     public void shouldSumUpEntries() {
         // given
         TimedCounter<String> counter = new TimedCounter<>(90, TimeUnit.SECONDS);
-        counter.entries.put("expired", new ExpiringMap.ExpiringEntry<>(800, 0));
-        counter.entries.put("expired2", new ExpiringMap.ExpiringEntry<>(24, System.currentTimeMillis() - 100));
+        counter.getEntries().put("expired", new ExpiringMap.ExpiringEntry<>(800, 0));
+        counter.getEntries().put("expired2", new ExpiringMap.ExpiringEntry<>(24, System.currentTimeMillis() - 100));
         counter.put("other", 10);
         counter.put("Another", 4);