Option to send send specif emails to admin OR to not send duplicate emails if admin is also staff

[Valentina R]

Ideally, a filter to remove admin as the receiver of the emails would be great.

In case admin is also a staff member, he gets the admin-new-appointment email twice. It should not send to the same email twice.

Requested here.

[Željan Topić]

Made emails unique from 4.7.6