add new EmailDomains API Commands for listing domain/email-usage information; show email-domain overview when customer has >1 domains with email addresses; add EmailDomains to GlobalSearch

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

lng/de.lng.php

@@ -1070,6 +1070,7 @@ Vielen Dank, Ihr Administrator',
 			'email' => 'E-Mail',
 			'emails' => 'Adressen',
 			'webmail' => 'Webmail',
+			'emailsoverview' => 'E-Mail Domain Übersicht',
 		],
 		'mysql' => [
 			'mysql' => 'MySQL',

lng/en.lng.php

@@ -1139,6 +1139,7 @@ Yours sincerely, your administrator',
 			'email' => 'Email',
 			'emails' => 'Addresses',
 			'webmail' => 'Webmail',
+			'emailsoverview' => 'Email domains overview',
 		],
 		'mysql' => [
 			'mysql' => 'MySQL',