Add css class qrlink to images on sponsorscanning landing page

This was already done on the other pages with QR codes, but somehow
these were missed.

Needed so a conference skin can avoid adding borders around them,
because borders on the images make QR readers not like them.

template.jinja/confsponsor/scanner_landing.html

@@ -46,7 +46,7 @@ <h3>Personal link</h3>
   Or scan this QR code:
 </p>
 <p>
-  <img src="data:image/png;base64,{{qrlink}}" />
+  <img class="qrlink" src="data:image/png;base64,{{qrlink}}" />
 </p>
 
 <p>
@@ -78,6 +78,6 @@ <h2>Test</h2>
   conference. You can find a code to test with at
 </p>
 <p>
-  <img src="data:image/png;base64,{{qrtest}}" />
+  <img class="qrlink" src="data:image/png;base64,{{qrtest}}" />
 </p>
 {%endblock%}