Adding a way to get the current timestamp in Cypher.

```
neo4j-sh (?)$ create (n {ts:gettimestamp});
+-------------------+
| No data returned. |
+-------------------+
Nodes created: 1
Properties set: 1
3 ms

neo4j-sh (?)$ start n=node(*) return (getTimestamp - n.ts) / 1000;
+------------------------------+
| (getTimestamp - n.ts) / 1000 |
+------------------------------+
| 29                           |
+------------------------------+
1 row
16 ms
```

Willing to accept feedback... especially on the name.