[SPARK-11086][SPARKR] Use dropFactors column-wise instead of nested loop when createDataFrame

Use `dropFactors` column-wise instead of nested loop when `createDataFrame` from a `data.frame`

At this moment SparkR createDataFrame is using nested loop to convert factors to character when called on a local data.frame.  It works but is incredibly slow especially with data.table (~ 2 orders of magnitude compared to PySpark / Pandas version on a DateFrame of size 1M rows x 2 columns).

A simple improvement is to apply `dropFactor `column-wise and then reshape output list.

It should at least partially address [SPARK-8277](https://issues.apache.org/jira/browse/SPARK-8277).

Author: zero323 <matthew.szymkiewicz@gmail.com>

Closes #9099 from zero323/SPARK-11086.