Added new environment variables for custom css, custom title, and custom description.

Fully tested using the Dockerfile, example can be found on https://fileshare.thenextweb.co.za

server/layout.js

@@ -40,6 +40,11 @@ module.exports = function(state, body = '') {
           type="text/css"
           href="${assets.get('app.css')}"
         />
+        <link
+          rel="stylesheet"
+          type="text/css"
+          href="${state.ui.assets.custom_css}"
+		/>
         <link
           rel="apple-touch-icon"
           sizes="180x180"