Improve error handling when loading timeout + eslint rules

[mondaychen]

When loading page timed out, we assume it's loaded instead of throwing. This is to handle cases when 1) there's bad link to analytics or ads scripts on the page 2) looping JS that keeps changing the page

Also, introduced new eslint rules no-throw-literal and prefer-promise-reject-errors to ensure we always have error.message to be shown to user