Separate data from code (closes #8)

[Roboe]

This was just finished in Roboe/fprsmap@7e08fa2, but I added Roboe/fprsmap@644f3de too because data is more readable formated as YAML, as we talked, than as JSON.

Preview: https://roboe.github.io/fprsmap

Changelog:

• Complete rewrite of fprsmap.js:
  • follow Airbnb's JavaScript Style Guide (EcmaScript 5)
  • clearly divide JavaScript sections, but keep the code in a single file
  • add fetch polyfill and query the communities JSON data (#8)
• Communities data:
  • formatted as YAML for easy external contributions (less error-prone syntax for non-coders)
  • sorted by forum post number, to track changes easily
• Security: Enabled SSL for map tiles (HTTPS)
• Security: Added Subresource Integrity (SRI) for the CDN's libraries

I've taken some decisions on my own, so any of the above points are open to discussion, of course, :)