Small cleanups / changes amassed over time

- Small javadoc fixes
- Simplifications
- Move logException method from StringUtils to ExceptionUtils

src/main/java/fr/xephi/authme/util/ExceptionUtils.java

@@ -33,4 +33,14 @@ public final class ExceptionUtils {
         }
         return null;
     }
+
+    /**
+     * Format the information from a Throwable as string, retaining the type and its message.
+     *
+     * @param th the throwable to process
+     * @return string with the type of the Throwable and its message, e.g. "[IOException]: Could not open stream"
+     */
+    public static String formatException(Throwable th) {
+        return "[" + th.getClass().getSimpleName() + "]: " + th.getMessage();
+    }
 }