Separate javascript from html

- Extract component javscript into the `source/javascripts/refills/`
- Rewrite snippet helpers to support javascript snippets
- Change import generator to also copy javascripts

https://trello.com/c/S5F4aAvv

@Magnus-G, this needs some design work. We are currently rendering two snippet divs if there is no js and three if there is. This causes the third snippet div to flow on a second line.