Introduce retina support to WordCamp.org

[melchoyce]

We request 926x160 banners for WordCamp, which are scaled and cropped to various other sizes around the site, but that small of a size looks really blown up and grainy on retina screens. We should introduce retina support for WordCamp banners and graphics on the WordCamp.org site and start requesting 2x images from WordCamp organizers.

See attached screenshot for evidence of blurry, non-retina images.

[iandunn]

I've updated the docs to request 1852x320. We'll still need to update the image sizes in Central's theme and maybe a few other things.

[juanfra]

Modified image size and added CSS to make it work with retina. (Don't know if we need to add a new size or by editing the 'wccentral-thumbnail-large' is fine).

[juanfra]

Hey guys,

I hope you are doing well. Patch submitted.

Cheers,
Juanfra.

[coreymckrill]

This appears to be fixed now, as long as the organizer uploads a large enough image.

[coreymckrill]

(Also, further enhancements to this will be addressed in the WC Central redesign)