Remove robot meta on note edit page and html template, add prevent crawling header to enhance note privacy

lib/response.js

@@ -123,7 +123,6 @@ function responseHackMD(res, note) {
         url: config.serverurl,
         title: title,
         useCDN: config.usecdn,
-        robots: (meta && meta.robots) || false, //default allow robots
         facebook: config.facebook,
         twitter: config.twitter,
         github: config.github,
@@ -135,7 +134,8 @@ function responseHackMD(res, note) {
     res.writeHead(200, {
         'Content-Type': 'text/html; charset=UTF-8',
         'Cache-Control': 'private',
-        'Content-Length': buf.length
+        'Content-Length': buf.length,
+        'X-Robots-Tag': 'noindex, nofollow' // prevent crawling
     });
     res.end(buf);
 }