Forms: Add subject, CC and BCC

Support
2

There is a bug for the mail subject. I currently think about/work on it.

Adding dynamic cc and bcc through the forms settings is complicated right now…

If you want to adjust cc and bcc in config.yaml, you have to write these options as an array:

# use smtp to send emails
mailer:
    from      : contactform@example.com
    transport : smtp
    host      : smtphost.provider.com
    user      : fancy-username
    password  : SuperSavePassword
    port      : 587
    auth      : true
    encryption: starttls
    cc        :
        support@example.com
    bcc       :
        admin@example.com