Collect Map added
Summary:
Tests are on the way. Please first comment if you're OK with this implementation, some points are discussable.
What works now:
```
bash:MEMGRAPH_ROOT/build/>./tests/manual/console 10
MG>MATCH (n) RETURN COLLECT("age_" + n.age, n.height)
+-----------------------------------------------------------------------------------------------------------------------------------+
| COLLECT("age_" + n.age, n.height) |
+-----------------------------------------------------------------------------------------------------------------------------------+
| {age_10: 176, age_13: 180, age_24: 172, age_25: 179, age_32: 123, age_33: 186, age_37: 147, age_43: 162, age_49: 126, age_6: 170} |
+-----------------------------------------------------------------------------------------------------------------------------------+
```
Reviewers: mislav.bradac, teon.banek, buda
Reviewed By: mislav.bradac, buda
Subscribers: pullbot
Differential Revision: https://phabricator.memgraph.io/D695
ca8fb55ac5