Icon updates

[laryn]

Some of the icons feel a bit dated (e.g. Google) -- and it might be nice to also provide an SVG icon option. We should be able to download the relevant .svg files from FontAwesome and use them here.

• https://github.com/FortAwesome/Font-Awesome/tree/master/svgs/brands

  Attribution is required by MIT, SIL OFL, and CC BY licenses. Downloaded Font Awesome Free files already contain embedded comments with sufficient attribution, so you shouldn't need to do anything additional when using these files normally.

[laryn]

There is some level of support for SVG already with the "Zocial" integration. Perhaps that can be extended to work better.