Create population.csv

Added data
Closes ukodi-training/ODP-Group1#3
Update index.html

Added map section
Closes ukodi-training/ODP-Group1#2
Update config.js

Added / defined the name of the data file and heading for population column
Update config.js

I forgot to close last change.
Closes ukodi-training/ODP-Group1#4
Merge pull request #6 from ianparfitt/gh-pages

Milestone 1 met