secure logo uploading, avoid frame-inclusion, adjustments to SECURITY.md and minor changes in UI for domain import and darkmode

Signed-off-by: Michael Kaufmann <d00p@froxlor.org>

lib/formfields/admin/domains/formfield.domains_import.php

@@ -55,6 +55,11 @@ return [
 					]
 				]
 			]
+		],
+		'buttons' => [
+			[
+				'label' => lng('domains.domain_import')
+			]
 		]
 	]
 ];