Add nonce to <script> elements

[Yannik]

This PR adds the configured nonce to <script> elements (or nothing, it no nonce is set, since getNonceAttribute will then return an empty string).

This does not fix all of the csp issues (embedded fonts, third party assets), but it atleast makes laravel-debugbar usable with a configured content security policy.

To set the nonce, you can use Debugbar::getJavascriptRenderer()->setCspNonce($yourNonce);

[Yannik]

Combined with maximebf/php-debugbar#561 (which has been merged), this fixes all script-src csp issues! style-src 'unsafe-inline' is still required, since there are a few inline styles where I haven't found a good solution yet.