Closes#268. Not going to bother with a preview SVG or anything fancy for now – we can think about that as part of #746. Right now it's just good to finally get this functionality in!
Also need to think about apple-touch-icon, msTile stuff, and social sharing image. Not sure if this is all too much for core, but it's definitely too much for the current Appearance page layout. Again, something to think about as part of #746.
Code is a bit rough around the edges, but figured there's not much point in using the command bus properly since #870.
- Get rid of Bootstrap (except we still rely on some JS)
- Use BEM class names
- Rework variables/theme config
- Fix various bugs, including some on mobile
The CSS is still not ideal – it needs to be cleaned up some more. But
that can be a focus for after beta.
