Updated PIC user guide to reflect API changes and added a simple Java example. The API is still not very Java-friendly. I created SPARK-5990 for this issue.

Author: Xiangrui Meng <meng@databricks.com>

Closes #4680 from mengxr/SPARK-5897 and squashes the following commits:

847d216 [Xiangrui Meng] apache header
87719a2 [Xiangrui Meng] remove PIC image
2dd921f [Xiangrui Meng] update PIC user guide and add a Java example