[IMP] res.partner: unused imports
[IMP] public_user: make parent partner inactive too
[IMP] orm: when a _constraint check raises, catch it and combine its message with the constraint message for the user-friendly popup

Plus minor cleanup
[FIX] ir.ui.view: restore extended validation of view arch, let exceptions bubble up to constraint checker, cleanup+translate error messages

Raising an exception in a _constraint will now be
properly considered as a failed constraint, and the
user will see a warning popup with the exception
message. Therefore it makes sense to translate the
error as well, at least the not-too-technical part