Add category for parking

[steffenrapp]

I'd like to enter a reservation for parking at the airport. Currently there's no dedicated category for it. I could add it as booking or transportation with type "Other" but that doesn't feel right. It would be great to have a separate type for that.
Booking might be a better fit as the location doesn't change.

[mauriceboe]

@steffenrapp coming in 4.0.0!