User Javascript can break functionality

[NeverDecaf]

If the Custom Javascript supplied in the extension's options throws an error, this can cause the js that is essential to the extension to not run correctly, which will break the PWA. (This may specific to the script I was using, as it tampers with discord's webpack.) The solution should be to catch and safely ignore errors caused by user js, though this poses an issue with unsafe-inline (see #28).

This is a partial duplicate of #28, which is essentially 2 separate issues.