Switch images to svgs, where possible (#1563)

Closes #1361, #1362

assets/img/svg/flags/so.svg

@@ -0,0 +1,11 @@
+<svg xmlns="http://www.w3.org/2000/svg" height="480" width="640" version="1">
+  <defs>
+    <clipPath id="a">
+      <path fill-opacity=".67" d="M-85.334 0h682.67v512h-682.67z"/>
+    </clipPath>
+  </defs>
+  <g clip-path="url(#a)" fill-rule="evenodd" transform="translate(80.001) scale(.9375)">
+    <path fill="#40a6ff" d="M-128 0h768v512h-768z"/>
+    <path d="M336.48 381.19l-82.505-53.476-82.101 54.001 30.535-87.754-81.95-54.188 101.39-.756 31.447-87.488 32.121 87.286 101.39.116-81.53 54.699 31.209 87.56z" fill="#fff"/>
+  </g>
+</svg>