fix: custom security class import, bad cast

[dpgaspar]

Description

when using a custom SecurityManager FAB raises:

    Type[BaseSecurityManager], security_manager_class
NameError: name 'BaseSecurityManager' is not defined

ADDITIONAL INFORMATION

• Has associated issue: NameError: name 'BaseSecurityManager' is not defined #1849
• Is CRUD MVC related.
• Is Auth, RBAC security related.
• Changes the security db schema.
• Introduces new feature
• Removes existing feature