Icon Font Update

Updated icon fonts to include. Docs to be updated after this PR is merged.
- Hamburger
- Plus
- Minus
- Grid view
- List view

Also moved the inline collection view JS into `shop.js`.

This lets us delete the inline svg icons previously used for collection views, while adding a few more commonly used icons to the set.

Edit: also moved collections and blog sidebars below main content with `grid--rev` on mobile sizes. Should be its own PR, but minor enough I tacked it on here.

@mpiotrowicz @stevebosworth 
does the icon need to be nested inside the `icon-fallback-text` element, or can it be placed outside?