CERN/LHCb branding

[alexpearce]

Adds CERN and LHCb logos to the page footer, and changes the typeface to PT Sans for headings and PT Serif for the rest. This matches what other CERN websites use (and it happens to look better, IMO).

The presence of the CERN logo is required in the CERN design guidelines, which websites asking for a .cern address must comply with, see #7 for discussion.

Couple of screenshots:

[kdungs]

Might be a stupid question but I know they are very strict about those things: are we entitled to use the CERN logo?

[kdungs]

Also your commit only contains @2x versions of the logo. Do you also want to include @4x and sans-@ versions and use something like retina.js or do you think that's just overkill?

[alexpearce]

Might be a stupid question but I know they are very strict about those things: are we entitled to use the CERN logo?

The design guidelines say:

The CERN logo is the property of the Organization. Its use is subject to autorisation (link sends e-mail).

We need the logo for the .cern domain. But really the approval for the domain and the approval to use the logo are the same thing: “this project is a proper CERN project”. I suggest we wait for the approval from the spokespeople (who @apuignav has contacted), and then we can open the ticket with CERN, showing them this PR.

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Also your commit only contains @2x versions of the logo. Do you also want to include @4x and sans-@ versions and use something like retina.js or do you think that's just overkill?

I do have the @1x versions locally, but I only included the @2x as the browser does a good-enough job of downscaling it to non-retina screens. Seeing as we only have the two images, and they both downscale well, I don't think we need retina.js yet.

I hadn't considered @4x at all. Is that for UHD monitor?