Allow rewriting sender address

This is useful when using an SMTP server as relay that only allows
a specific sender address.
Allow relaying mails to local users

This allows relaying all mails to users like root and cron to a
specific mail address.
Allow sending a test mail on configuration changes

Send a test mail to a specified address after Postfix is restared.
Clean up some whitespace
Merge branch 'feature/sender_rewrite_and_others' of https://github.com/meeee/ansible-postfix into develop

Conflicts:
	tasks/install.deb.yml
Update contributors
Bump version: 1.1.1 → 2.0.0