[SPARK-13734][SPARKR] Added histogram function

## What changes were proposed in this pull request?

Added method histogram() to compute the histogram of a Column

Usage:

```
## Create a DataFrame from the Iris dataset
irisDF <- createDataFrame(sqlContext, iris)

## Render a histogram for the Sepal_Length column
histogram(irisDF, "Sepal_Length", nbins=12)

```
![histogram](https://cloud.githubusercontent.com/assets/13985649/13588486/e1e751c6-e484-11e5-85db-2fc2115c4bb2.png)

Note: Usage will change once SPARK-9325 is figured out so that histogram() only takes a Column as a parameter, as opposed to a DataFrame and a name

## How was this patch tested?

All unit tests pass. I added specific unit cases for different scenarios.

Author: Oscar D. Lara Yejas <odlaraye@oscars-mbp.usca.ibm.com>
Author: Oscar D. Lara Yejas <odlaraye@oscars-mbp.attlocal.net>

Closes #11569 from olarayej/SPARK-13734.