Added WhatsApp social button

James right now I'm hard coding the content character of the what's app icon into the .f-button.whats-app selector. Seems kind of dirty since we're generating the font in the other repo, not sure what's the best thing to do. 

Note: For now, I'm hardcoding some whatsapp CSS in the main fundly app until we get this merged.

https://github.com/fundly/fundly-icon-font/pull/1