Prevent users from focusing outside the modal when it's open

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 1.5.x
• Fix Version/s: 2.0.x, 1.5.x, master, 2.5.x, 1.5.2.12, 2.0.0.18-deprecated, 1.5.2.15, 3.1.x
• Component/s: Dialog (deprecated), JavaScript
• Labels: None
• Git Pull Request: https://github.com/natecavanaugh/alloy-ui/pull/272

The user is currently able to focus on elements behind the modal, though only when they're inside iframes. This change adds code to prevent this by changing all iframes on the page to have a tabIndex value of -1. It restores the tabIndex attribute when the modal is closed.