Refactored the UsageAgreement page

The demo text has been substituted and the interface has changed
a little bit. No more tab panel but radiobuttons. The usage
agreement text is not hardcoded anymore but stays in the locales
files as the rest of the content.

All the anchors now open a new window.

The clickable objects that might try to change the app content by
addressing the document.location.href are now intercepted. This
cannot be blocked but the user is asked whether to proceed or not.