Use correct theming when returning the defaults

[nickvergessen]

Fix#3148

To test with firefox/chrome, just remove the following lines:

server/lib/private/Security/CSP/ContentSecurityPolicyNonceManager.php

Lines 69 to 71 in 7d221ff

	Request::USER_AGENT_CHROME,
	// Firefox 45+
	'/^Mozilla\/5\.0 \([^)]+\) Gecko\/[0-9.]+ Firefox\/(4[5-9]|[5-9][0-9])\.[0-9.]+$/',

cc @LukasReschke@MorrisJobke

Should backport to 11

[MorrisJobke]

Tested and works 👍

[MorrisJobke]

cc @schiessle@blizzz@juliushaertl@LukasReschke