[session] move context manager logic in the security context manager The `init_security` and `reset_security` method have no other user that the context manager itself. Having dedicated public function is not useful.

[session] hook control context directly use transaction object when applicable Most of the hooks control logic have been moved on Transaction anyway.

[session] move context manager logic in the hook controls context manager The `init_hooks_mode_categories` and `reset_hooks_mode_categories` have no other user that the context manager itself. Having dedicated public function is not useful.

[session] drop the useless set_hooks_mode method It has not external user and trivial code

[session/transaction] move most undo support into transaction A small part that need repo access has not been moved into transaction yet.

[session] simplify mode property We can delegate very thing to transaction utility

[session/transaction] pass the session object to the Transaction __init__ This simplify access to variables. As we are moving more and more logic and states in the Transaction it will greatly helps in future commit.