Create plot1.R

"plot1.R" function creates a histogram of "Global Active Power" in PNG format
data source: UC Irvine Machine Learning Repository, electric power consumption
date range over 2 day period is used, i.e. from 2007-02-01 to 2007-02-02
Revert "Create plot1.R"

This reverts commit 1696ce4feb68d4d398cebb0f9bb268526fc28898.