- Updates favicons to use the new Tudor crown.
- Removes apple-touch-icon sizes that are no longer in common use.
- Adds SVG favicon.
- Adds manifest file and icons for Android devices.

The assets used in this commit are not final and are subject to change.

We anticipate that some servers may not be configured to correctly serve the .webmanifest content-type, so we're gonna stick with the (seemingly now legacy) .json
extension for now.

The `maskable` keyword tells Android devices that the icon has been designed with a circular, central safe area, and that Android launchers can
safely crop the edges of the icon instead of shrinking the icon down:
https://css-tricks.com/maskable-icons-android-adaptive-icons-for-your-pwa/

Despite the name, these are not 'masks' in the same way as the Safari icon. The Safari icon is an alpha mask, which is indicated using the
`monochrome` keyword instead.