Implement Content Secure Policy

[lonnieezell]

Per the specs, implement helper functions for CSP. This would likely be additional methods in the Response class to handle it. It looks like this will likely require the use of a separate class, if only to provide a way to work with nonces for script and style tags.

[lonnieezell]

A slightly more digest-able read about CSP can be found at http://www.html5rocks.com/en/tutorials/security/content-security-policy/.

[lonnieezell]

Added in 9c6972a