Generic pop-up boxes

[lknapp]

When checking for updates or disabling private wifi, the UI uses standard javascript confirm() / alert() popups. These don't match the look & feel of the rest of the site, and should be replaced with better-styled popups / modals.

[michellereamy]

got a screenshot of an example popup as it appears today?

[michellereamy]

pls mark with UI task label