Add demisexual flag

[inga-lovinde]

Add demisexual flag please? It is sorely needed and is present in other popular packs (e.g. blobhaj) but not with blobcats :(
I think it's the only popular flag missing (besides progress pride, but it will probably not work well on a blobcat)

SVG (taken from wikipedia) is:

<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 800 480">
  <path fill="#D2D2D2" d="M0 0h800v480H0"/>
  <path fill="#6E0070" d="M0 0h800v280H0"/>
  <path fill="#FFF" d="M0 0h800v200H0"/>
  <path d="M0 0l306 240L0 480"/>
</svg>