Better link tracking

The `module:clickstream:click` event now emits an object: 
{
  target: [the `a` or `button` element ancestor of the actually clicked element], 
  samePage: [Boolean],
  sameHost: [Boolean],
  tag: ["the | link | name | string"],
}
 
To specify that an element has "same page" behaviour, you can add the class `control` it. This disambiguates things like `<a href="/top-stories">`, which despite looking like an off-page link is turned into a same-page controller by js.