## What changes were proposed in this pull request?

JIRA issue: https://issues.apache.org/jira/browse/SPARK-13038

1. Add load/save to PySpark Pipeline and PipelineModel

2. Add `_transfer_stage_to_java()` and `_transfer_stage_from_java()` for `JavaWrapper`.

## How was this patch tested?

Test with doctest.

Author: Xusen Yin <yinxusen@gmail.com>

Closes #11683 from yinxusen/SPARK-13038-only.