Make `FormatValidator.ValidateContent` to verify payload of `LOCK`
objects. Pass locked objects to `Locker` interface. Require from
`Locker.Lock` to return `apistatus.IrregularObjectLock` error on a
corresponding condition.
Also add error return to `DeleteHandler.DeleteObjects` method. Require
from method to return `apistatus.ObjectLocked` error on a corresponding
condition. Adopt implementations.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
ced854bc2e