Mail: added DKIM signer

[lukaspijak]

• bug fix? no
• new feature? yes
• BC break? no

Hello,

this is the implementation of DKIM signatures into emails, see https://en.wikipedia.org/wiki/DomainKeys_Identified_Mail

In Nette is problematic to implement this feature, so I'd like to help it.

$sender = new Nette\Mail\SendmailMailer();

$sender->setSigner(new Nette\Mail\DkimSigner([
	'domain' => 'nette.org',
	'selector' => 'key1',
	'privateKey' => '__PRIVATE_KEY__',
], [
    'To', 'From', 'Subject', 'Date'
]));

$sender->send(new Nette\Mail\Message());

[dg]

Oh, thanks!