Make Cookie Banner compliant

[marcoow]

We are currently simple display the cookie banner but track users with GA anyway. I don't think that's compliant with the law really and we'd have to delay any tracking until the user actively consents.

Tasks

• [ ] extract JS code in lib/google-analytics/index.js into a (global) function that's not invoked immediately
• [ ] invoke global function when users consents to cookie usage (see https://github.com/simplabs/simplabs.github.io/blob/master/src/ui/components/CookieBanner/template.hbs#L8) – it would make sense to rename that to @onConsent or so
• [ ] if the cookie banner is invisible anyway (isCookieBannerVisible === false), invoke the global function lazily (using requestIdleCallback) from the Simplabs component's constructor

[marcoow]

This doesn't really make sense. If we do this (which I think we have to), the data we get from GA will be completely irrelevant as it only represents a (small) fraction of our actual traffic. Instead, we should probably remove GA altogether and use Netlify Analytics instead which works without JS, cookies etc.