fix(www): middle click on agreement links

[lukaslihotzki]

This PR fixes middle click on agreement links (to open it in a new tab without switching). It also fixes the validation error showing up when just clicking on a link. Furthermore, it makes the code more consistent (use router-link everywhere instead of $router.resolve, use target="_blank" everywhere instead of window.open).

[peterthomassen]

Thanks, just one minor question. Otherwise lgtm!