Implement stronger content-security-policy except in /pad/ which does not allow it.

Implement a "loader" which allows for applying a version number to everything.
Added a cache control for anything which has a version.

www/common/cryptpad-common.js

@@ -1,5 +1,5 @@
 define([
-    '/api/config?cb=' + Math.random().toString(16).slice(2),
+    '/api/config',
     '/customize/messages.js?app=' + window.location.pathname.split('/').filter(function (x) { return x; }).join('.'),
     '/customize/fsStore.js',
     '/bower_components/chainpad-crypto/crypto.js?v=0.1.5',