Currently we have two problems that are resolved by this change.

The first is that we have a dependency on Google Fonts, which means
that should it ever go down, or it have issues we would also have
issues. This will resolve this by moving the dependencies we load from
there to the local server.

The second issue is that Google Fonts is currently returning the
`local()` css font source. This causes a problem where the users browser
fails to fallback to a missing glyph, resulting in many unusual
characters displaying the failure glyph. This will resolve this by
creating a font-family definition that does not use the `local()`
source.

I did not update the error pages with local fonts, they still use the
remote google fonts api, so they're a self contained page that does not
use the asset pipeline.

This resolves tootsuite/mastodon#531 and tootsuite/mastodon#12

This allows other platforms such as Windows, macOS and iOS to use their system fonts rather than downloading a copy of Roboto. It also makes the app feel a little closer to native on those platforms!

Fix #205, fix #156, fix #124