Adds a new security header for Content-Security-Policy.

[jwoertink]

Purpose

Fixes #1664

Description

This PR adds a new Security module to set the Content-Security-Policy header.

/cc. @bararchy

Checklist

• - An issue already exists detailing the issue/or feature request that this PR fixes
• - All specs are formatted with crystal tool format spec src
• - Inline documentation has been added and/or updated
• - Lucky builds on docker with ./script/setup
• - All builds and specs pass on docker with ./script/test

[bararchy]

Looking good 🎉

[matthewmcgarvey]

Is this something we'd want users to set themselves or could we update the BrowserAction in lucky-cli with this?

[jwoertink]

hmmm 🤔 Part of me feels like this could be added by users individually since we've never had it before... but I also kind of feel like we could add it and it would fix crystal-loot/exception_page#17 ? maybe also related #1324