Fix Google AdSense

[gtirloni]

It seems that the ads are not working (neither in HTTP nor HTTPS mode). This PR should fix that.

• Switches from sync to async Google Adsense code
• Use HTTPS (so requests aren't blocked when accessing AChecker over HTTPS)

I'm not sure if the tracking code is correct and/or who has access to that, just using the ones that were already in the code.