TAJO-774: Implement logical plan part and physical executor for window function.

This patch adds the logical planning part, distributed planning part, and sort-based window aggregation physical executors. They enables Tajo to use existing aggregation functions in OVER clause and add row_number() and rank().

This implementation has some limits. First of all, this patch does not support multiple different partition key groups in a query.

Example:
```
SELECT rank OVER(PARTITION BY P ORDER BY K), avg OVER( PARTITION BY P) ...
```

In above case, a query contains two OVER clauses which have the same PARTITION KEY group. So, it becomes available in this patch. But, the following case is not available.

```
SELECT rank OVER(PARTITION BY P ORDER BY K), avg OVER( PARTITION BY W) ...
```

In addition, there is one limit. This patch does not support the definition clause for window specification. I'll add this feature later.

The followings are examples provided by this patch.
```
SELECT sum(l_quantity) OVER () FROM LINEITEM

SELECT l_orderkey, l_quantity, sum(l_quantity) OVER (PARTITION BY l_orderkey) FROM LINEITEM

SELECT l_orderkey, l_discount, sum(l_discount) OVER (PARTITION BY l_orderkey), sum(l_quantity)             OVER (PARTITION BY l_orderkey) FROM LINEITEM

SELECT l_orderkey, l_partkey, rank() OVER (ORDER BY l_orderkey) r1, rank() OVER(ORDER BY l_partkey desc) r2 FROM LINEITEM
```
How about override hashCode()? This class overrides equals(Object), but does not override hashCode().