Implement CSRF protection

- Added `useCsrf` composable for managing CSRF tokens and adding it automatically to axios requests.
- Refresh CSRF token refresh on Login/Logout.
- Updated templates to include CSRF meta tags.
- Custom CSRF session storage key removed. Slim Guard default storage is used. Prevent duplication of token in the session (persistent token option wasn't working)
- Fixes old session file not being deleted from the filesystem

Author: lcharette