dep: Add showdown (markdown-to-html converter)

Also add package-lock file to git repo

package.json

@@ -13,6 +13,7 @@
         "extend": "^3.0.1",
         "mysql": "~2.15.0",
         "pubsubhubbub": "~0.4.1",
+        "showdown": "^1.8.6",
         "winston": "2.4.2",
         "ws": "5.1.1",
         "xmldom": "^0.1.27"