This PR:
- Updates the ordering of embed codes to be as robust as possible.
- Updates the social media embed meta attributes to reflect some changes in Open Graph and Twitter embed rules.
- Adds a generic fallback for schema.org, which should also work with Google+.
- Adds an icon treatment specifically for social sharing.
- Updates the favicon to not use dark blue, as that's no longer part of the site palette.
The current avatar image we use is rendered a little weird in certain contexts:
Slack
So hopefully the new square treatment will get us looking our best!