See jio@24b938cb

Should fix most of the cases where reloading components cause breakage.
There is still a race condition between a transaction's cache being
actually flushed (which can only happen at transaction boundaries) and
another transaction doing the actual class reload, which will
immediately affect all the started transactions in the same process.

Once a portal type class became available again, instances of this classes
should no longer be broken and can be modified again

Some other types (Gadget Type) are currently lacking the interaction workflow
which resets the dynamic classes.

Persons created before the introduction of ERP5 Login and user_id will only
have a user_id after migration if they were already user before migration,
otherwise they will not have a user_id and creating assignments and ERP5 Login
for this person creates a user which can not log in the system.

To make it possible for these persons to login anyway, we ensure person has a
user id when validating a login

while setting an initial user id should be allowed for any user which can
create a person, changing an already set user id can have security
implications, so we protect it with a more strict permission

user_id are technical things that should not be displayed to users.

In the case of tokens, for now we show "something that's not user id / not the
token secret". That's not ideal but as far as I know whe don't really have use
cases of tokens to show a page where user caption would be displayed.

Person.setUserId is heavy, it serializes person module to prevent concurrency,
but in some cases we the risk of having duplicate user ids is under control, so
we don't want to pay the performance price.

See merge request !1242

See merge request nexedi/erp5!1243

padding too much in buttom make header bigger, so when export to pdf, header is cut off to hit heigth which make logo display at top