Click outside of a modal to close it and add 'x' button

[chris-huggins]

Many users click on the 'i' button on the people picker many times, repeatedly opening and closing modals. They appear to often click on the background, and take time to find the 'cancel' button, which is often used to close the menu without adding the Editor.

To ease this interaction slightly we should close the modal when the background/overlay is clicked, and should add a 'x' button to the top right of the modal (assuming this is an often expected interaction they could be looking for before finding cancel).