feat: special handling when displaying svg

one should probably display the defined symbols.

e.g. the format of icon we currently use is like this:

``` svg
<svg>
  <symbol id="symbol-1">...</symbol>
  <symbol id="symbol-2">...</symbol>
  <symbol id="symbol-3">...</symbol>
  <symbol id="symbol-4">...</symbol>
</svg>
```

we should probably have a list of defined symbols if the svg we're about to display is of this particular form...