Lock opened record

[jmartinm]

When a record is opened, it should be locked while the session is active so that no other user can open it.

For this, we can implement server side handlers in https://github.com/inveniosoftware-contrib/invenio-record-editor that will deal with locking and unlocking.

The locking information can be stored either in DB (new table needed) or in Redis. Advantage of Redis is that querying it is faster and we can set an expiration time.

[harunurhan]

@jmartinm what's the progress on this issue, as far as I remember you were doing something?