Disable Gravatar (#37)

* Disable Gravatar
* Lowercase emails
* Add migration

public/main.ts

@@ -2,6 +2,7 @@ import 'highlight.js/styles/tokyo-night-dark.css';
 import './style.css';
 import './markdown.css';
 import './favicon.svg';
+import './default.png';
 import moment from 'moment';
 import md from 'markdown-it';
 import hljs from 'highlight.js';