After introduction of LOCK objects (of type `TypeLock`) complicated
extended its behavior:
* create `lockers` container bucket (LCB) during PUT;
* remove object from LCB during DELETE;
* look up object in LCB during EXISTS;
* get object from LCB during GET;
* list objects from LCB during LIST with cursor;
* select objects from LCB during SELECT with '*'.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
Implement `DB.Lock` method which marks list of the objects as locked by
another object. Only regular objects can be locked.
Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>
