Better handling of Google Analytics

[ndorfin]

This PR:

• Removes the inline script from the base template
• Adds the GA script in the main JS manifest
• Will only invoke GA if DoNotTrack is not set to 1.

See: https://developer.mozilla.org/en-US/docs/Web/API/Navigator/doNotTrack

[mermop]

To be honest I haven't done DNT before - the MDN article you link to does note it's an experimental technology - are there any browser compatibility issues we might come across?

Should be fine though

[ndorfin]

With this polyfill:

function DNT () {
   if ('msDoNotTrack' in navigator) return navigator.msDoNotTrack;
   if ('doNotTrack' in window)      return window.doNotTrack;
   if ('doNotTrack' in navigator)   return navigator.doNotTrack;
   return 0;
 };

…we're saying: If your browser doesn't support DNT, then we'll set your DNT policy to 0 (or Track me by default). But if your browser does support DNT, through one of the 3 APIs we check for, then we'll check what your DNT status is. If DNT is 1, we don't load GA. If DNT is 0 (default) we'll load GA.

[mermop]

Right - should be fine then - let's put it up