Loss of focus on feature pop up

[AliyanH]

When you tab into a feature pop up, if you keep pressing tab the focus will exit out of the pop up rather than going back to the first element.

When you tab into the "zoom to here" link and press shift-tab, the popup loses focus and the focus is shifted to the feature itself.

This is a bug in how focus is managed withn the feature popup (aka button). The tab / shift+tab keys should move around the popup controls but never exit the popup. You should only exit the popup when you dismiss it or press next/previous buttons in the popup controls. However we noticed that focus drifts outside the popup by accident. For example, steps to reproduce:

Load this page
Tab to the first feature (tab x 2)
Hit enter to activate the popup
Tab x 1
Shift+Tab x 1
What you expect to happen: focus should be on the X (dismiss) button
What happens: focus returns to the feature, leaving the popup displayed

Originally posted by @prushforth in #163