Fix round avatar images in gamegraph

[stingray21]

see

https://ishadeed.com/article/new-facebook-css/

<svg role="none" style="height: 36px; width: 36px;">
  <mask id="avatar">
    <circle cx="18" cy="18" fill="white" r="18"></circle>
  </mask>
  <g mask="url(#avatar)">
    <image x="0" y="0" height="100%" preserveAspectRatio="xMidYMid slice" width="100%" xlink:href="avatar.jpg" style="height: 36px; width: 36px;"></image>
    <circle cx="18" cy="18" r="18"></circle>
  </g>
</svg>