Pixmenia v19 Persistent Assets Update

- Added includes/persistent_assets.php
- Added pixboost_app/includes/persistent_assets.php
- Updated pixboost_app/includes/config.php
- Added pixboost_app/admin/persistent_assets.php
- Added sql/v19_persistent_assets.sql
- Patched pixboost_app/enhance.php with persistent assets include

PHP syntax:
PASS