* add doc for spark
* labelCol equals to label by default
* change title and reformat
* reference about default index type
* fix doc build
* Update website/docs/Examples/Integrate - Spark.md
* update doc
* Added more references
* remove exception case when `y_train.name` is None
* fix broken link
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Co-authored-by: Wendong Li <v-wendongli@microsoft.com>
Co-authored-by: Li Jiang <bnujli@gmail.com>
