Host our own fonts, don't get them from mozilla.org

[pascalchevrel]

Out of convenience, we fefch fonts from mozilla.org but mozilla.org servers are in the US, slow for us localizers in EMEA and a lot of our initial page load time is getting them.

Let's host them ourselves on Transvision, potentially I might look at using Fira Sans instead of OpenSans since it seems mozilla is transitionning to that on the middle term.