[SPARK-2965][SQL] Fix HashOuterJoin output nullabilities.

Output attributes of opposite side of `OuterJoin` should be nullable.

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #1887 from ueshin/issues/SPARK-2965 and squashes the following commits:

bcb2d37 [Takuya UESHIN] Fix HashOuterJoin output nullabilities.
[SPARK-2968][SQL] Fix nullabilities of Explode.

Output nullabilities of `Explode` could be detemined by `ArrayType.containsNull` or `MapType.valueContainsNull`.

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #1888 from ueshin/issues/SPARK-2968 and squashes the following commits:

d128c95 [Takuya UESHIN] Fix nullability of Explode.
[SPARK-2650][SQL] Build column buffers in smaller batches

Author: Michael Armbrust <michael@databricks.com>

Closes #1880 from marmbrus/columnBatches and squashes the following commits:

0649987 [Michael Armbrust] add test
4756fad [Michael Armbrust] fix compilation
2314532 [Michael Armbrust] Build column buffers in smaller batches