High-contrast icons for accessibility branch

@alice This is my first stab at the HC star icons. I'm almost certain I've messed them up somehow :) Could you take a look and let me know if there are changes that need to be made?

We'll probably want to reference whatever we do end up using in the stylesheet per the doc.

PS: As this currently refs the other work you've done you may want to just pull these in manually if we do use them.