Contact form: Created mailer base class.
Contact form: Created system and SMTP mailers.
Contact form: Removed old way of sending through SMTP.
Contact form: Changed settings form to include mailer selection.
Contact form: Removed obsolete mailing methods and adapted to new mailer system.
Backend: User manager: Use mailer system instead of contact form methods.
Leads: Removed mailing support.

No longer needed as contact form can do all this now.
Shop: Use mailer system.
Contact form: Implemented getRecipient and getTemplate methods.
Contact form: Fixed bugs.