Dfoxpowell/track plan type

we were already tracking signin

```js
window.analytics.track('account sign in', {
  category: 'account',
  label: w.location.pathname
}, {
  Marketo: true
});
```

added tracking based upon `subscription_plan` not being null

IMPORTANT: this is off of the https://github.com/optimizely/marketing-website/pull/419 PR because alot of JS changed so merge 419 first