feat: markdown XSS protection, better dropdown UX

package-lock.json

package.json

src/components/annoucements/Announcement.jsx

src/components/mde/MarkdownEditor.jsx

src/components/posts/Post.jsx

src/components/posts/PostList.jsx

src/markdown.js

src/pages/Home.jsx

src/utils.js

src/ws/handlers/posts.js

typings/cf2021.d.ts