Summary:
Before this change, unique constraints supported only pairs of label
and a single property. With this change, unique constraints can be
created for label and set of properties.
Better tests for unique constraints in general are also included in
this diff.
Reviewers: mferencevic, teon.banek
Reviewed By: mferencevic
Subscribers: pullbot
Differential Revision: https://phabricator.memgraph.io/D2653
95c9755e13