Dev mode & code location

[adrexia]

https://github.com/rafaeldsousa/silverstripe-securityheaders/blob/415fc9a61126a532a2bd47f89b49feaad5a692eb/src/extensions/SecurityHeadersExtension.php#L24

Could we remove this line, and enable/disable from yml instead? It's a lot easier to change a yml property to exclude dev than it is to switch environments over to test/live mode, and a more obvious place to look when debugging.

Namespaces: can we either change the composer namespace to rafaeldsousa, or move to the dnadesign github? It will make it more obvious where to look for this code

[rafaeldsousa]

@adrexia yep, lets do all of that, but first move the package to the dna repo (we'll just need to update all sites using this to point to that repo instead).