review existing modal accessibility + replace it with polyfilled native dialog element

[alpower]

Look at the accessibility of our existing modal solution, and possibly replace it with a dialog modal:

Nice overview w a react compatible polyfill I reckon we should look at this as super-accessible out of box https://www.viget.com/articles/the-dialog-element/

Current Modal isn't very accessible e.g. on a cursory glance you cannot close it with the keyboard using the X) and the escape key doesn't allow closing) and tabbing allows focus down to elements on the page behind.

see demo of http://edenspiekermann.github.io/a11y-dialog/example/ in comparison