#806 Create period cleanup task and implement cleanup for session records

src/main/java/fr/xephi/authme/initialization/HasCleanup.java

@@ -0,0 +1,14 @@
+package fr.xephi.authme.initialization;
+
+/**
+ * Common interface for types which have data that becomes outdated
+ * and that can be cleaned up periodically.
+ */
+public interface HasCleanup {
+
+    /**
+     * Performs the cleanup action.
+     */
+    void performCleanup();
+
+}