erp5_core: Add External method to access getSecurityCategoryFromAssignmentParentFunctionParentGroup from extensions.erp5.StandardSecurity

Without this script is not possible access the method to generate security policy which will be able to combine parent (for group and function) plus strict base category

Added a security policy which is able to combine parent (for group and function) plus strict base category. It can be useful to generate groups as function* + group* + site, for example.

Predicate security is checked at higher levels

Inventory API does not depend on security
Also fix some pylint complains

smtp_url can be None, so do not treat it as string, allow to take different
actions (like doing nothing).

getMessageList shall not be available on normal mail host. It will be available
on one coming from live tests, so in such case die immediately.