Allow chart.css to work as-is on the site's charts and embedded charts.
Add quick intro to embedded graphs to README.
Add embed.css for style rules that are specific to embedded graphs.
Import charts.css from embed.css.
Merge branch 'upstream-updates' into embeddable-widgets
Use wazimap's Google Analytics key on embedded graphs.
Remove duplicate static files. Use 'embed_data' folder exclusively for the embedded data files.
Update Nginx config to serve files from 'embed_data' directory.