Fixes swagger-editor/#1502.

Change logic for markdown rendering to:

1. Convert source markdown to HTML
2. Sanitize HTML
3. Send sanitized HTML to markdown renderer

package.json

@@ -42,6 +42,7 @@
     "base64-js": "^1.2.0",
     "brace": "0.7.0",
     "classnames": "^2.2.5",
+    "commonmark": "^0.28.1",
     "css.escape": "1.5.1",
     "deep-extend": "0.4.1",
     "expect": "1.20.2",
@@ -72,6 +73,7 @@
     "redux": "^3.x.x",
     "redux-immutable": "3.0.8",
     "redux-logger": "*",
+    "remarkable": "^1.7.1",
     "reselect": "2.5.3",
     "sanitize-html": "^1.14.1",
     "scroll-to-element": "^2.0.0",