Remove google plus icon from branding bar

[heyitsolivia]

While we're at it, we may be able to drop IE8 support and stop using the iconfont from sf-icons by replacing them with SVGs—fewer requests and smaller file size (which seems like a win-win for me).

[jalbertbowden]

do we have the svgs or do i need to get them?

[heyitsolivia]

You can find the svg version of the icons in the iconfonts here: https://github.com/sunlightlabs/sf-icons/tree/master/src/fonts