add focus on modal for a11y

[LindsayYoung]

Keyboard navigation accessibility issue for the modal.

Expected behavior:
While the modal is open focus should stay within the modal.

Current behavior:
When the touchpoints the modal opens up, the focus isn't on the form so people have to tab through the page to get to the form. This is causing an accessibility issue.

Example:
The focus is on "here's how you know" link behind the modal, It would then go through all the links to get to the form.(It is a little hard to see but it was the best visual example I could find.)

[ryanwoldatwork]

thanks @LindsayYoung!

I'll provide status on this next week.