sec: Move the CSP to a header on the nginx

frontend/src/index.hbs

@@ -4,7 +4,6 @@
     <title>Lateinicus</title>
 
     <meta charset="UTF-8">
-    <meta http-equiv="Content-Security-Policy" content="default-src 'self'; script-src 'self' https://unpkg.com; img-src 'self'; img-src 'self' https:; font-src https://fonts.googleapis.com https://fonts.gstatic.com; style-src 'self' https://fonts.googleapis.com 'unsafe-inline';">
     <meta
       name="viewport"
       content="minimum-scale=1, initial-scale=1, width=device-width, shrink-to-fit=no"