Refactored ticket price handling(see desc)

* Events do not have a price any more. Instead, they point to a ticket
type
* Ticket types have prices
* Store sessions have quantity and ticket type.

Should be ready to implement payment system soon, but i want to wait
until i am back on stable internet for it.

TODO: I broke some stuff in these commits. I need to update my local dev
server, and fix what i have broken. Will try to do on airplane