Fixes and updates

- Add CSP policy to fix youtube embeds
- Remove twitter timeline
- Add nightly build link to download page

Change-Id:If17ec8dbd1de435c9a0caedf4daa7ae6ebe3c5b2
Reviewed-on: https://asterix-gerrit.ics.uci.edu/c/incubator-asterixdb-site/+/19070
Reviewed-by: Ian Maxon <imaxon@apache.org>
diff --git a/content/community.html b/content/community.html
index 2f676e6..96b1175 100644
--- a/content/community.html
+++ b/content/community.html
@@ -8,6 +8,7 @@
     <meta name="description" content="">
     <meta name="author" content="">
     <link rel="icon" href="favicon.ico">
+    <meta http-equiv="Content-Security-Policy" content="frame-src youtube.com www.youtube.com">
 
     <title>Community</title>