Set the cost of an order to the price of what is being bought on creation
Implement total drink cost function
Show drinks and accounts on buy drink page

- Include extra information for both the drink and the account
- Filter accounts and drinks bought in the past to the current event so only relevant accounts are shown
- Don't show anything if there are no events (create no form choices)
Fix display error in registration complete page
Don't throw an invalid type exception when someone hasn't bought a drink yet
Use the proper counter so labels actually have a number in their for field
Make a function to return the last event instead of copy/pasting some hardcoded numbers