Show Reservation Core Information in Ticket Email

Add a section at the top in the email incl.:
- What (resource)
- When (date and time)
- (Price)

<img width="588" alt="mail" src="https://user-images.githubusercontent.com/186856/57460897-44f31700-7276-11e9-912e-b59876a4d812.png">

<img width="1366" alt="web" src="https://user-images.githubusercontent.com/186856/57460934-52a89c80-7276-11e9-945b-5e2751d99f89.png">

