Convert images to webp

[KhafraDev]

With a lossy format, we can trim the image sizes down nearly 85% if we pushed it.

At minimum, we should be able to reliably push a 50% size reduction without losing too much quality (and more if we resize images correctly).

Things to consider:

• Much faster loading times on slow connections.
• Safari has limited support for webp.

[Razenpok]

You can also create a texture atlas to further reduce load times: https://www.gamasutra.com/view/news/177857/Building_an_HTML5_game_Dont_shrug_off_atlases.php