#792 #814 Implement SQLite migration, allow last IP to be nullable in MySQL

- Old SQLite setups have the last IP column as NOT NULL but without a default value. With the new concept (where we don't set a last IP on player registration) it fails.
  - Create an /authme debug child that allows to migrate SQLite (tricky because SQLite does not support dropping or modifying columns)
  - Allow last IP column to be NOT NULL in MySQL as well (extend MySQL /authme debug child)
- Add TODO comments with follow-up issue to extend our commands with new registration IP field

src/main/java/fr/xephi/authme/permission/DebugSectionPermissions.java

@@ -32,6 +32,9 @@ public enum DebugSectionPermissions implements PermissionNode {
     /** Permission to change nullable status of MySQL columns. */
     MYSQL_DEFAULT_CHANGER("authme.debug.mysqldef"),
 
+    /** Permission to perform a migration of SQLite. */
+    MIGRATE_SQLITE("authme.debug.migratesqlite"),
+
     /** Permission to view spawn information. */
     SPAWN_LOCATION("authme.debug.spawn"),