Jetty configuration wiki page and configuration to help mitigate clickjacking

[Cantor, Scott]

> Please let me know if you would like me to change anything or revert.

More to the point, I could use feedback or additional requirements around the feature in 3.4. It looks like I need to generalize or extend the CSP properties to allow that to be set more openly.

I did look at full CSP but as I noted in JIRA, that appeared to be a nightmare of ridiculous proportions based on what I could find on portability of non-inline JS.

-- Scott