Use favcount.js v1.0.1

As a followup to #1348, I pulled out the favicon notification stuff into its own library: [**favcount.js**](http://chrishunt.co/favcount)

Not a huge deal for Discourse, but the library no longer depends on jQuery and [is versioned](https://github.com/chrishunt/favcount/releases) :sparkles:

I would like to get this merged so that any issues with find with favicon notification in the future can get fixed upstream as well.