Implement support for @cloak-app/visual

[weotch]

As described in BKWLD/cloak-visual#2, the dependence on @nuxt/image makes it hard to use @cloak-app/visual outside of Nuxt. Right now I pass $img into the $cloakImg() helper:

https://github.com/BKWLD/cloak-visual/blob/36b7cacf4bdbdf7c217fb19c05cef5dfd76533f3/plugins/helpers.js#L30

I'll need to make my own $img function that supports the same API and reads presets and config from the Nuxt config 😓 .