Add LaTeX / math input and rendering support (#345)

* Initial display support

* Use better colors for error in math parsing

* Parse math markdown

* Use proper jsx

* Better copy support

* use css var directly

* Remove console.debug call

* Lazy load math module

* Show fallback while katex is loading

src/app/atoms/math/Math.jsx

@@ -0,0 +1,33 @@
+import React, { useEffect, useRef } from 'react';
+import PropTypes from 'prop-types';
+
+import katex from 'katex';
+import 'katex/dist/katex.min.css';
+
+import 'katex/dist/contrib/copy-tex';
+import 'katex/dist/contrib/copy-tex.css';
+
+const Math = React.memo(({
+  content, throwOnError, errorColor, displayMode,
+}) => {
+  const ref = useRef(null);
+
+  useEffect(() => {
+    katex.render(content, ref.current, { throwOnError, errorColor, displayMode });
+  }, [content, throwOnError, errorColor, displayMode]);
+
+  return <span ref={ref} />;
+});
+Math.defaultProps = {
+  throwOnError: null,
+  errorColor: null,
+  displayMode: null,
+};
+Math.propTypes = {
+  content: PropTypes.string.isRequired,
+  throwOnError: PropTypes.bool,
+  errorColor: PropTypes.string,
+  displayMode: PropTypes.bool,
+};
+
+export default Math;

src/app/molecules/message/Message.jsx

@@ -189,7 +189,7 @@ const MessageBody = React.memo(({
   let content = null;
   if (isCustomHTML) {
     try {
-      content = twemojify(sanitizeCustomHtml(body), undefined, true, false);
+      content = twemojify(sanitizeCustomHtml(body), undefined, true, false, true);
     } catch {
       console.error('Malformed custom html: ', body);
       content = twemojify(body, undefined);