Summary:
This diff contains a basic implementation of unique constraints consistent with
the MVCC storage.
Stale records in the unique constraints are collected by the garbage collector.
Tests for checking correctness of unique constraints and violations are included.
Note: currently we only support a pair of label and a single property. Support for
multiple properties will be added later.
Reviewers: mferencevic, teon.banek
Reviewed By: mferencevic, teon.banek
Subscribers: buda, ipaljak, pullbot
Differential Revision: https://phabricator.memgraph.io/D2608
e2e7823ec4