move data to separate file; add link field to data; save locations to…

[alpiepho]

… local storage

I am just starting to learn data visualization and really like how you used D3. I made a couple modifications toward porting for other projects. The first mini-project using this can be found at
https://alpiepho.github.io/state-web-development-2018-2019-withD3-static/

Thanks again for sharing your work,
Al

[trongthanh]

Thanks, but this feature is not necessary for my case. Besides, I'd like to keep all JS in one file to reduce unnecessary requests and optimize load time.

However, I'll leave this PR open in case others visit this repo and find it useful.