Links within tours should open in a new tab

[wolfmanstout]

If content within a tour is hyperlinked to an external site, it should open in a new tab. For example, the image on page 2 of the Cat tour takes me to Wikipedia in the current tab, but it should open in a new tab instead.

[lentinj]

This is related to https://github.com/OneZoom/OZtree/issues/869, where we need to intercept such links and show a QR code (at least that's what I think we should do).

Opening in a new tab seems like a reasonable default though.