Enhancements to SEO form

This PR adds a forgotten a/b test result, legacy success tracking via pageviews, and enhances the usage/error tracking of the form. Changes:

1. Adds auto focus to the `#url-input` field because this increased conversions in an a/b test (except on touch devices)
2. Adds `/account/create/success` and `/free-trial/success` legacy "events"/pageviews in GA
2. Switches the API response time over to the GA user timing API instead of event tracking since user timing was made to track time
3. Makes the number of validation errors per submit easier to see in GA by storing it in the label value
4. Increases the /edit redirect from 500ms to 1s to ensure that all tracking events get sent out before the navigation changes
5. Handles the JSON.parse error better

**Verifying the auto focus**:

Load /free-trial and verify that `#url-input` is focused on page load.

**Verifying the legacy success events/pageviews**:

Load /free-trial, submit it successfully, look for these events:

```
ea:Viewed /free-trial/success Page
```

```
Viewed /account/create/success Page
```

**Verifying the user timing**:

Load /free-trial, open your network console (click preserve log), fill out the form, then filter your network requests for "collect". You should see an event that has these parameters: 

```
utc:api response time
utv:/account/free_trial_create
utt:24
```

utc = user timing category
utv = user timing value
utt = user timing time (this is the actual time so it will vary)

**Verifying the number of errors per submission**:

Submit the /free-trial form with bad data in one or more fields. Look for this event in the network log:

```
ec:form error
ea:seo-form validation error
el:3 errors
```

ec = event category
ea = event action
el = event label (if you didn't put anything in any of the fields you should see three, otherwise this number should match the number of validation errors you forced)