Accessibility focus issues with the modal

[roebuk]

Describe the bug
When the Everfund modal is activated the users focus should be brough into the modal. Whilst the modal is open, the users keyboard focus should be unable to escape contents of the modal. Upon close of the modal the focus should be restored to button that activated the modal.

To Reproduce
Steps to reproduce the behaviour:

1. Open the model, the focus remains on the button that activate the modal.
2. Tab around and eventually you'll be able to tab outside of the modal.
3. Close the modal and you're focus isn't taken back the activating button.

Expected behavior
The focus behaviour should match the WAI-ARIA authoring practices on modals

[BurnedChris]

Thanks for opening this issue @roebuk,

I will start looking into this, my only thoughts right now until I move into it, is

1. is this a problem with both the @everfund/react-sdk and @everfund/js-sdk,
2. look to change the focus to a child of an iframe? (is that possible, I guess so)