Summary:
With quite frequent changes of serialization backend, it's getting
really painful updating the C++ implementation. This diff defines the
Symbol class via LCP, so that the C++ serialization is generated instead
of written by hand.
Reviewers: mtomic, llugovic
Reviewed By: mtomic
Subscribers: pullbot
Differential Revision: https://phabricator.memgraph.io/D1741