cache static assets for 3 hours at least (#242)

* cache static assets for 3 hours at least

* moving _headers to the static folder

web/static/_headers

@@ -0,0 +1,20 @@
+/*.css
+  Cache-Control: public, max-age=10800
+
+/*.js
+  Cache-Control: public, max-age=10800
+
+/*.png
+  Cache-Control: public, max-age=10800
+
+/*.jpg
+  Cache-Control: public, max-age=10800
+
+/*.svg
+  Cache-Control: public, max-age=10800
+
+/*.gif
+  Cache-Control: public, max-age=10800
+
+/*
+  X-Frame-Options: DENY