errata-symbol-customizable isn't customizable on puzzle pages

[Vroo]

https://github.com/PuzzleServer/mainpuzzleserver/wiki/Event-Customization

It should be customizable on both. Since rendering of emoji characters varies on different systems, it should be replaceable and that's hard to do with the current structure. For index, the html structure should be:

<span class="errata-customizable" title="This puzzle has errata"><span class="errata-symbol-customizable">⚠<span></span>

For puzzles, it should be:

<span class="errata-customizable" title="This puzzle has errata"><span class="errata-symbol-customizable">⚠<span>Text of errata</span>

with

errata-symbol-customizable { color: red; font-weight: 700; }

in the site css.