Issue: #3 using official Mailchimp API V2

You will need composer
Use the new functionality for BackendModel::getModuleSettings()
Ping to Mailchimp API V2
Use mailEngine to send preview mailing
Use mail engine for saving mailing draft
getClientsAsPairs from Mailchimp API V2
Return false when no mail engine set
Sort list names
No mail engine set
Add mail_engine to start
Choose address list
Choose mail engine settings
Locale updated
Mailchimp API V2 integrated
Camelcased variable
Set mail engine to mailchimp when set
getAccountDetails from Mailchimp API V2
getCustomFields from Mailchimp API V2
Create campaign using Mailchimp API V2
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