Bulk Operation

SPARK-9427 Make `column` and `col` functions be S4 functions

SPARK-9427 Add `when` expressino function in SparkR

SPARK-9427 Add window functions into SparkR

SPARK-9427 Update `NAMESPACE` file in SparkR for simple parameters functions

SPARK-9427 Add `struct`, `encode` and `decode` function in SparkR

SPARK-9427 Add expression functions into SparkR which have a variable parameter

SPARK-9427 Add expression functions into SparkR which conflict with the existing R's generic

SPARK-9427 Add expression functions into SparkR whose params are complicated

SPARK-9427 Add expression functions into SparkR whose params are simple