Remove dependency on WebGL

[yushih]

The rotating icosahedron, shown when something is loading, depends on WebGL. If WebGL is not supported by the browser, unhandled exceptions are thrown and a blank screen is shown. This is not a huge problem since 92.32% (https://caniuse.com/#search=webgl) of all users have WegGL. Nevertheless, it is good to have some fallback method for indicating loading and avoid blocking the other 7.68% users.