[SPARK-12025][SPARKR] Rename some window rank function names for SparkR

Change ```cumeDist -> cume_dist, denseRank -> dense_rank, percentRank -> percent_rank, rowNumber -> row_number``` at SparkR side.
There are two reasons that we should make this change:
* We should follow the [naming convention rule of R](http://www.inside-r.org/node/230645)
* Spark DataFrame has deprecated the old convention (such as ```cumeDist```) and will remove it in Spark 2.0.

It's better to fix this issue before 1.6 release, otherwise we will make breaking API change.
cc shivaram sun-rui

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #10016 from yanboliang/SPARK-12025.