Code to get data and unzip it into data subdirectory

Make sure we're consistently checking for the raw data files.  if they
all do not exist, we get the zip file and unzip it into the data
subdirectory
added readAndMergeData method to create one, merged data frame

Commented out lines for unneeded files to get data and added method for
reading the data from the test and train data files and merge them into
one data frame