Switch to use system fonts

[formgeist]

The current font used in the UI is Roboto. I'd like to make the suggestion to switch to use system fonts.

Here's a few arguments for switching from Roboto to using system fonts;

• The system fonts on Mac San Francisco and Windows Segoe UI are very close to Roboto. Even on mobile where San Francisco are used for iOS and Roboto for Android.
• Having to add a custom font as an asset seems contrived when you have great system fonts already ready at your disposal.
• Monospace variants come for free as well.

There's a few caveats to be aware of;

• Ubuntu (Linux) has their own Ubuntu system font (http://font.ubuntu.com/) which deviates quite a bit from the other aforementioned in it's style and even legibility.
• The branding of the UI will not be as connected to the Elastic brand.

I think it would be great, at least as an experiment, to have a branch of the EUI which uses system fonts to test it out on different platforms to see the results. This also means testing weights, sizes and more. We can probably do with just using BrowserStack or something similar to do screengrabs and share them in this issue.

Thoughts?

@elastic/eui-design

[snide]

I'm on board for this and I LOVE taking out anything someone needs to download. In my tests I could barely tell the difference. Think branding is probably the bigger question mark here.

[formgeist]

Created a PR for the implementation #127

[Michalwo]

This is not an issue from the brand side. We had already shifted away from Open Sans to Roboto in order to optimize the in-product experience. This continues on that path. So this means that SF will be the default font in all Sketch files? I'm assuming we're all on Macs.

[snide]

Cool. Sketch is mac only, so not an issue there either.

[gjones]

I like this too.

[bevacqua]

Loving this from my side as well. Great teamwork you guys 🎉