Support storing match pattern in a variable

[jamesfer]

When using MATCH, the path pattern can be stored in a variable for use in FOREACH clauses or other functions.

Possible implementation could be:

query.match('path', [
  node('person'),
  relation('out', [ 'FriendsWith' ]),
  node('friend'),
])
// MATCH path = (person)-[:FriendsWith]->(friend)